build: linux mingw cross-compile fixes (partial)

Enables the Linux -> win-x64 MinGW cross-compile path that got broken
after recent merges. Still INCOMPLETE — build fails later at missing
DirectX IME headers (DIMM.h) and likely more vendor SDK compat issues.
Commit captures the mechanical fixes so Jakub can adopt/iterate.

Changes:

1. toolchains/linux-mingw64.cmake — MinGW cross-compile toolchain
   (Windows x86_64 target, mingw-w64 gcc/g++/windres, lld linker).

2. CMakeLists.txt:
   - MSVC-only flags (/MP, /Zi, /DEBUG linker flag) gated behind
     if(MSVC) — they break MinGW gcc which treats /MP as filename.
   - UNICODE / _UNICODE defined globally (was inside if(MSVC), but
     WIN32_FIND_DATA etc. need it everywhere).
   - __int64 -> long long compile definition for non-MSVC compilers
     so the Granny SDK header parses.
   - -mssse3 compile option for non-MSVC so _mm_shuffle_epi8 in
     EterLib/GrpImageTexture.cpp inlines correctly.

3. Include fixes for Linux case-sensitive filesystem and stricter
   GCC standard library:
   - Poly/StdAfx.h: backslash in include path -> forward slash.
   - EterBase/Stl.h: <SSTREAM> -> <sstream>.
   - EterBase/Utils.h: add <cmath> so cos() in templates resolves.
   - AudioLib/MaSoundInstance.h: add <cstdint> so uint8_t vector
     template argument is valid.
   - AudioLib/Type.h: add <cstdint> for uint32_t.
   - extern/include/utf8.h: add <cstdint> for uint8_t/uint16_t.
   - EffectLib/Type.h: typedef typename std::vector<...>::iterator
     (dependent-name C++11+ compliance).

Not committed (needs manual recreation per checkout, or git-tracking
them needs buy-in):
   - 60+ stdafx case-variant symlinks (stdafx.h, StdAfx.h, Stdafx.h)
   - 7 directory case symlinks (Eterlib, eterLib, eterBase, Gamelib,
     gamelib, Eterbase, eterbase)
   - header case-variant symlinks in individual dirs

Still failing at:
   - src/EterLib/IME.h:7 wanting DIMM.h (DirectX IME, not in extern/
     and not shipped with mingw-w64). Needs either a shim header, a
     #ifdef _MSC_VER guard, or vendoring the Microsoft DirectX IME SDK.

Work done over ~2h trying to get a fresh release cycle through from
Linux. Stopping here because each fix exposes another vendor/compat
issue that benefits from Jakub's context of the build history.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/EffectLib/Type.h

@@ -217,7 +217,7 @@ extern BOOL GetTokenTimeEventFloat(CTextFileLoader & rTextFileLoader, const char
 template <typename T>
 void InsertItemTimeEvent(std::vector<CTimeEvent<T> >* pTable, float fTime, T fValue)
 {
-	typedef std::vector<CTimeEvent<T> >::iterator iterator;
+	typedef typename std::vector<CTimeEvent<T> >::iterator iterator;
 
 	iterator itor = std::lower_bound(pTable->begin(), pTable->end(), fTime);