Stop DCC from complaining about it's own additions with -Wextra enabled

[Dylan-Brotherston]

This is a fix for issue #65

This PR will stop DCC from emitting the following errors about its own additions with -Wextra enabled

<stdin>:869:59: error: unused parameter 'envp' [-Werror,-Wunused-parameter]
static void launch_valgrind(int argc, char *argv[], char *envp[]) {
                                                          ^
<stdin>:1025:30: error: unused parameter 'a' [-Werror,-Wunused-parameter]
void _Unwind_Backtrace(void *a, ...) {
                             ^
<stdin>:1068:20: error: comparison of integers of different signs: 'int' and 'unsigned long' [-Werror,-Wsign-compare]
        for (int i = 0; i < sizeof buffer/sizeof buffer[0]; i++)
                        ~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<stdin>:1435:20: error: comparison of integers of different signs: 'int' and 'size_t' (aka 'unsigned long') [-Werror,-Wsign-compare]
        for (int i = 0; i < size; i++) {
                        ~ ^ ~~~~
<stdin>:1436:63: error: comparison of integers of different signs: 'unsigned long' and 'int' [-Werror,-Wsign-compare]
                if (max_stdout_bytes && n_actual_line + n_actual_bytes_seen > max_stdout_bytes) {
                                        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~
<stdin>:1595:20: error: comparison of integers of different signs: 'int' and 'unsigned long' [-Werror,-Wsign-compare]
        for (int i = 0; i < sizeof buffer/sizeof buffer[0]; i++)
                        ~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<stdin>:1601:20: error: comparison of integers of different signs: 'int' and 'unsigned long' [-Werror,-Wsign-compare]
        for (int i = 0; i < sizeof line_buffer/sizeof line_buffer[0]; i++)
                        ~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

DCC will still produce the following errors about it's own additions with -Weverything enabled

<stdin>:35:9: error: macro name is a reserved identifier [-Werror,-Wreserved-id-macro]
#define _GNU_SOURCE
        ^
<stdin>:258:8: error: padding size of 'struct cookie' with 4 bytes to alignment boundary [-Werror,-Wpadded]
struct cookie {
       ^
<stdin>:580:24: error: implicit conversion changes signedness: 'ssize_t' (aka 'long') to 'size_t' (aka 'unsigned long') [-Werror,-Wsign-conversion]
        size_t n_bytes_read = read(cookie->fd, buf, size);
               ~~~~~~~~~~~~   ^~~~~~~~~~~~~~~~~~~~~~~~~~~
<stdin>:602:9: error: implicit conversion changes signedness: 'size_t' (aka 'unsigned long') to 'ssize_t' (aka 'long') [-Werror,-Wsign-conversion]
        return n_bytes_read;
        ~~~~~~ ^~~~~~~~~~~~
<stdin>:614:27: error: implicit conversion changes signedness: 'ssize_t' (aka 'long') to 'size_t' (aka 'unsigned long') [-Werror,-Wsign-conversion]
        size_t n_bytes_written = write(cookie->fd, buf, size);
               ~~~~~~~~~~~~~~~   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
<stdin>:623:9: error: implicit conversion changes signedness: 'size_t' (aka 'unsigned long') to 'ssize_t' (aka 'long') [-Werror,-Wsign-conversion]
        return n_bytes_written;
        ~~~~~~ ^~~~~~~~~~~~~~~
<stdin>:645:9: error: implicit conversion loses integer precision: 'off_t' (aka 'long') to 'int' [-Werror,-Wshorten-64-to-32]
        return result;
        ~~~~~~ ^~~~~~
<stdin>:895:21: error: variable length array used [-Werror,-Wvla]
        char *valgrind_argv[valgrind_command_len + argc + 1];
                           ^
<stdin>:940:33: error: this function declaration is not a prototype [-Werror,-Wstrict-prototypes]
static void disable_check_output();
                                ^
                                 void
<stdin>:941:29: error: function '__dcc_error_exit' could be declared with attribute 'noreturn' [-Werror,-Wmissing-noreturn]
void __dcc_error_exit(void) {
                            ^
<stdin>:964:21: error: this function declaration is not a prototype [-Werror,-Wstrict-prototypes]
void __asan_on_error() NO_SANITIZE;
                    ^
                     void
<stdin>:971:44: error: this function declaration is not a prototype [-Werror,-Wstrict-prototypes]
        extern char *__asan_get_report_description();
                                                  ^
                                                   void
<stdin>:972:34: error: this function declaration is not a prototype [-Werror,-Wstrict-prototypes]
        extern int __asan_report_present();
                                        ^
                                         void
<stdin>:966:6: error: no previous prototype for function '__asan_on_error' [-Werror,-Wmissing-prototypes]
void __asan_on_error() {
     ^
<stdin>:964:6: note: this declaration is not a prototype; add 'void' to make it a prototype for a zero-parameter function
void __asan_on_error() NO_SANITIZE;
     ^
                     void
<stdin>:986:6: error: no previous prototype for function '_Unwind_Backtrace' [-Werror,-Wmissing-prototypes]
void _Unwind_Backtrace(void *a, ...) {
     ^
<stdin>:964:6: note: this declaration is not a prototype; add 'void' to make it a prototype for a zero-parameter function
void __asan_on_error() NO_SANITIZE;
     ^
                     void
<stdin>:986:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
void _Unwind_Backtrace(void *a, ...) {
^
static 
<stdin>:993:7: error: no previous prototype for function '__asan_default_options' [-Werror,-Wmissing-prototypes]
char *__asan_default_options() {
      ^
<stdin>:964:6: note: this declaration is not a prototype; add 'void' to make it a prototype for a zero-parameter function
void __asan_on_error() NO_SANITIZE;
     ^
                     void
<stdin>:986:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
void _Unwind_Backtrace(void *a, ...) {
^
static 
<stdin>:993:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
char *__asan_default_options() {
^
static 
<stdin>:1008:6: error: no previous prototype for function '__ubsan_on_report' [-Werror,-Wmissing-prototypes]
void __ubsan_on_report(void) {
     ^
<stdin>:964:6: note: this declaration is not a prototype; add 'void' to make it a prototype for a zero-parameter function
void __asan_on_error() NO_SANITIZE;
     ^
                     void
<stdin>:986:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
void _Unwind_Backtrace(void *a, ...) {
^
static 
<stdin>:993:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
char *__asan_default_options() {
^
static 
<stdin>:1008:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
void __ubsan_on_report(void) {
^
static 
<stdin>:1038:7: error: no previous prototype for function '__ubsan_default_options' [-Werror,-Wmissing-prototypes]
char *__ubsan_default_options() {
      ^
<stdin>:964:6: note: this declaration is not a prototype; add 'void' to make it a prototype for a zero-parameter function
void __asan_on_error() NO_SANITIZE;
     ^
                     void
<stdin>:986:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
void _Unwind_Backtrace(void *a, ...) {
^
static 
<stdin>:993:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
char *__asan_default_options() {
^
static 
<stdin>:1008:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
void __ubsan_on_report(void) {
^
static 
<stdin>:1038:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
char *__ubsan_default_options() {
^
static 
format, arg);
<stdin>:1200:60: error: format string is not a string literal [-Werror,-Wformat-nonliteral]
    int n = vfprintf(debug_stream ? debug_stream : stderr, format, arg);
                                                           ^~~~~~
fatal error: too many errors emitted, stopping now [-ferror-limit=]
<stdin>:964:6: note: this declaration is not a prototype; add 'void' to make it a prototype for a zero-parameter function
void __asan_on_error() NO_SANITIZE;
     ^
                     void
<stdin>:986:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
void _Unwind_Backtrace(void *a, ...) {
^
static 
<stdin>:993:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
char *__asan_default_options() {
^
static 
<stdin>:1008:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
void __ubsan_on_report(void) {
^
static 
<stdin>:1038:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
char *__ubsan_default_options() {
^
static