Fix MSVC build breaks on origin/main (stdarg.h va_list, mnmaps.c #-in-macro-arg)

[JRickey]

Summary

Two pre-existing MSVC build breaks have been blocking Windows RelWithDebInfo builds since the src/ → decomp/ submodule migration (#129) landed. Reproduce on a clean checkout of origin/main with no other patches applied.

What was broken

(1) decomp/include/stdarg.h — va_list __builtin_va_list redefinition on MSVC

The #ifndef __sgi block re-#defines va_list __builtin_va_list. MSVC has no __builtin_va_list intrinsic, so this fires C2061 (syntax error: identifier '__gnuc_va_list') cascading from the __GNUC_VA_LIST typedef.

MSVC fully sets up va_* via <vadefs.h> + __crt_va_* in the existing #ifdef _MSC_VER block at the top of the file, so it just needs to skip the GCC-builtin branch AND the IDO #else branch (the IDO branch would re-typedef char* va_list after vadefs.h already typedef'd it).

Fix: wrap both the GCC-builtin and IDO branches in #ifndef _MSC_VER.

(2) decomp/src/mn/mnmaps/mnmaps.c:1073 — #ifdef PORT inside macro arg list

#ifdef PORT directives sit inside the lbRelocGetFileData(...) argument list. lbRelocGetFileData is a function-like macro defined in src/lb/library.h:

#define lbRelocGetFileData(type, file, offset) \
    ((type) ((uintptr_t)(file) + (intptr_t)(offset)))

The C standard says # directives inside function-like macro args are undefined behavior. Clang/gcc accept leniently, MSVC rejects with C2059 (syntax error: '#') regardless of /Zc:preprocessor (the conforming preprocessor turns it into a C5101 warning AND a C2059 error).

Fix: hoist the PORT/non-PORT conditional values into local variables before the macro call so the macro args themselves are directive-free. Same end semantics, no behavior change — it's purely a textual/structural fix to satisfy the C-standard rule on macro-arg preprocessor directives.

Scope

A tree-wide scan for #ifdef PORT at non-zero paren depth turned up 30 candidate sites in 11 files, but 29 of them sit inside regular function calls (which MSVC's preprocessor accepts because the rule only applies to function-like macro args, not function args). Only the two #ifdef PORTs in mnmaps.c needed restructuring. No other files affected.

Test plan

• Clean origin/main + this branch on Windows (MSVC 19.44.35225): build error before — error C2061: syntax error: identifier '__gnuc_va_list' and error C2059: syntax error: '#'. Build succeeds after, produces BattleShip.exe.
• Bytes-equivalent change: mnmaps.c fix is purely a hoist of compile-time-conditional values out of a macro arg list. Local-variable values are identical to the inline expressions they replace, both for PORT and non-PORT branches. No runtime behavior change.
• Linux/macOS unaffected: clang/gcc were already accepting both constructs; the #ifndef _MSC_VER guard makes the GCC-builtin branch fire identically as before, and the mnmaps.c hoist is just a refactor. Cross-platform CI would confirm.
• Game smoke: launch the produced BattleShip.exe, verify VS match boots and a Training-mode wallpaper renders (the only path the mnmaps.c hoist touches).

Submodule pointer bump

Decomp pushed to JRickey/ssb-decomp-re#agent/msvc-build-fixes at commit 62ba3fd23. Outer commit 69b912b bumps the submodule pointer.

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