Allow disabling IPO for large generated game runners

[GTTeancum]

Summary

• add a default-on PS2X_ENABLE_RUNNER_IPO option
• let EnableFastReleaseMode retain the normal Release optimizations while omitting /GL, /LTCG, and CMake IPO for one target
• apply that opt-out only to ps2EntryRunner; runtime libraries keep their existing IPO behavior

Motivation

Large statically generated game targets can exhaust linker memory even with a single link worker. A 107-translation-unit X-Men Legends runner exceeded a 2 GiB linker-process cap with IPO enabled. Disabling IPO only for the generated runner allowed the complete executable to link under the same cap while preserving /O2 and optimized/IPO-enabled runtime libraries.

The option defaults ON, so existing builds are unchanged.

Validation

Configured current upstream main with MSVC/Visual Studio 2022, CMAKE_BUILD_TYPE=Release, and global IPO enabled:

• PS2X_ENABLE_RUNNER_IPO=OFF: generated ps2EntryRunner.vcxproj has no WholeProgramOptimization or LinkTimeCodeGeneration; ps2_runtime.vcxproj still has whole-program optimization.
• PS2X_ENABLE_RUNNER_IPO=ON: the runner again has whole-program optimization and LTCG, preserving the default behavior.

The 107-unit game runner was compiled with /O2 and no /GL, linked with /CGTHREADS:1 under the unchanged 2 GiB guard, passed PE section validation, and reached rendered gameplay.