Comment out compiler builtins

[davispuh]

Consider C header like:

#define va_copy __builtin_va_copy
#define ALIGNOF(TYPE)  _Alignof (TYPE)
#define __unused  __attribute__((__unused__))
#define __noreturn  __attribute__((__noreturn__))
#define STATIC_ASSERT  _Static_assert
#define CONST  const
#define STATIC  static
#define __volatile  volatile

Currently dsep would produce:

enum va_copy = __builtin_va_copy;

Which fails to compile:

Error: undefined identifier `__builtin_va_copy`
enum va_copy = __builtin_va_copy;

When this PR is applied together with #303
Then result will be:

// FIXME: enum va_copy = __builtin_va_copy;
// FIXME: alias ALIGNOF = _Alignof;
// FIXME: enum __unused = __attribute__(__unused__);
// FIXME: enum __noreturn = __attribute__(__noreturn__);
// FIXME: enum STATIC_ASSERT = _Static_assert;
// FIXME: enum CONST = const;
// FIXME: enum STATIC = static;

[Copilot]

Pull request overview

This PR updates macro translation output so that macros which expand to C compiler builtins/keywords/attributes (and therefore generate invalid D code) are emitted as commented-out // FIXME: lines instead of uncompilable declarations, aligning with the behavior introduced in #303.

Changes:

• Detect compiler builtins (e.g., __builtin_*) and _Alignof in function-alias macro translation and prefix the generated alias with // FIXME:.
• Detect keyword/attribute-like macro values (e.g., const, static, _Static_assert, __attribute__*) in alias/const macro translation and prefix the generated declaration with // FIXME:.
• Avoid repeated translation of the same macro expression by storing the translated value once.

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[jacob-carlborg]

There's no test added.