Fix FormatMessageA trampoline generation#139
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FormatMessageA takes a va_list pointer. On 64-bit targets, Clang canonicalizes va_list as an array of __va_list_tag, so the generated helper prototype tried to spell a pointer-to-array type as a simple parameter and produced invalid C syntax. Treat array pointees as opaque in best-effort helper prototypes: the trampoline only needs the outer pointer ABI, and void * preserves that ABI without depending on the host va_list representation. Enable the existing shim and add a fixture that exercises reordered ANSI string inserts through a real guest va_list. Implement only the minimal FORMAT_MESSAGE_FROM_STRING insert path needed by the test; broader FormatMessageA support remains out of scope.
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FormatMessageA is needed for error diagnostics in MSVC 4.2 (and possibly other tools from that era). E.g. RC.EXE currently errors because the function is not available. Note that the existing implementation is not feature-complete - this PR focuses only on enabling the function and giving it enough functionality to verify that the va_list works.
FormatMessageA takes a va_list pointer. On 64-bit targets, Clang canonicalizes va_list as an array of __va_list_tag, so the generated helper prototype tried to spell a pointer-to-array type as a simple parameter and produced invalid C syntax. Treat array pointees as opaque in best-effort helper prototypes: the trampoline only needs the outer pointer ABI, and void * preserves that ABI without depending on the host va_list representation.
Enable the existing shim and add a fixture that exercises reordered ANSI string inserts through a real guest va_list. Implement only the minimal FORMAT_MESSAGE_FROM_STRING insert path needed by the test; broader FormatMessageA support remains out of scope.