Allow C macros in CN specs

[thatplguy]

The C preprocessor doesn't expand macros in comments, which means CN specs (in comments) can't use C macros. It would be nice to make this possible, although there are challenges; see rems-project/cerberus#230 (comment).

[peterohanley]

This would also help with macros that replace a symbol, like here: https://github.com/GaloisInc/VERSE-OpenSUT/blob/8e0db300668301b92578f19f559ce09eae714426/components/mission_protection_system/src/variants/instrumentation_handwritten_C.c#L4

We need to refer to it here: https://github.com/GaloisInc/VERSE-OpenSUT/blob/8e0db300668301b92578f19f559ce09eae714426/components/mission_protection_system/src/include/instrumentation.h#L114 but we can't because we can't access the name. Frama-C doesn't mention the name for specs on declarations so it doesn't have this problem.