[esrrhs]

Why

CMakeLists.txt pinned Windows/MinGW to -O0, while Linux and macOS use -O3
(and -O0 only for USE_COV builds). No comment or commit message explains the
exception: git log -S'-O0' -- CMakeLists.txt traces it back to the initial tree,
carried over by 01c2ed23 (Replace the repository with fakelua master).

In practice CMAKE_BUILD_TYPE=Release appends CMAKE_CXX_FLAGS_RELEASE
(-O3 -DNDEBUG) after CMAKE_CXX_FLAGS, so GCC saw
... -g3 -ggdb3 -fPIC -O0 -O3 -DNDEBUG ... and used -O3 anyway. The -O0
only took effect for builds without a build type, which made Windows
inconsistent with Linux and the intent misleading.

Change

• Remove the IF (WIN32) branch; Windows now shares the ELSE () branch with
  Linux: USE_COV=ON -> -O0, otherwise -O3 (both C and C++).
• Add a comment documenting the shared policy.
• Net: 2 insertions, 5 deletions in the root CMakeLists.txt.

Verification (Windows / MSYS2 MINGW64, GCC 14.2, Ninja)

• Configure: compile flags now contain -O3 and no -O0 (grep FLAGS build.ninja).
• Full cmake --build of fakelua + flua is run locally and covered by CI.

Note: CMAKE_BUILD_TYPE=Release builds were already effectively -O3 before
this change, so release binaries are unaffected; only unconfigured builds now
get the intended optimization level (with the usual -O3 + -g3 cost in build
time and binary size).

[esrrhs]

Local verification is complete (Windows / MSYS2 MINGW64, GCC 14.2.0, CMake 3.31.2, Ninja):

• Configure: build.ninja compile flags now contain -O3 and no -O0.
• Full cmake --build --parallel 6 (457 targets: fakelua, flua and all CPM deps): passed in 14m7s.
• Smoke test on the fresh artifacts: flua install_check.lua --once --jit_type=1 -> init ok / fini ok, exit code 0.

No source changes were needed beyond the root CMakeLists.txt. Release builds were already effectively -O3 before this PR, so installed binaries are unaffected; this change makes unconfigured builds consistent and removes the misleading flag.

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.75%. Comparing base (6f54d8d) to head (f6afaf2).
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Additional details and impacted files

@@           Coverage Diff           @@
##           master      #52   +/-   ##
=======================================
  Coverage   89.75%   89.75%           
=======================================
  Files         125      125           
  Lines       27231    27231           
=======================================
  Hits        24441    24441           
  Misses       2790     2790           

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