[OKL] Adds @directive preprocessor attribute

[dmed256]

Description

When using stringification macros such as OCCA_JIT, there is no way to add preprocessor directives such as

OCCA_JIT(
  props,
  (entries, a, b, ab),
  (
    for (int block = 0; block < entries; block += 16; @outer) {
      #pragma ivdep
      for (int i = block; i < (block + 16); ++i; @inner) {
        ...
      }
    }
  )
)

Introducing @directive which replaces

#pragma ivdep

with

@directive("#pragma ivdep")

resulting in the code looking like:

OCCA_JIT(
  props,
  (entries, a, b, ab),
  (
    for (int block = 0; block < entries; block += 16; @outer) {
      @directive("#pragma ivdep")
      for (int i = block; i < (block + 16); ++i; @inner) {
        ...
      }
    }
  )
)

[codecov]

Codecov Report

Merging #246 into master will increase coverage by 0.09%.
The diff coverage is 85.04%.

@@            Coverage Diff             @@
##           master     #246      +/-   ##
==========================================
+ Coverage    71.9%   71.99%   +0.09%     
==========================================
  Files         276      276              
  Lines       19290    19376      +86     
==========================================
+ Hits        13870    13950      +80     
- Misses       5420     5426       +6

Impacted Files	Coverage Δ
src/lang/macro.cpp	81.91% <0%> (ø)	⬆️
src/lang/tokenizer.cpp	79.65% <40%> (+0.03%)	⬆️
src/lang/preprocessor.cpp	72.09% <90.62%> (+2.59%)	⬆️
src/lang/specialMacros.cpp	60.16% <0%> (+0.84%)	⬆️