The CFLAGS_x86_64_pc_windows_msvc env-var approach from 990b6f1 did
nothing — cargo-xwin ships its own clang-cl cmake toolchain file at
~/.cache/cargo-xwin/cmake/clang-cl/x86_64-pc-windows-msvc-toolchain.cmake
which hardcodes COMPILE_FLAGS and FORCE-overrides CMAKE_C_FLAGS. Any
env-var CFLAGS gets dropped before opus's cmake build sees it.
The only place that actually makes it into every C file compilation
in the libopus subbuild is the toolchain file itself. Patch it in
place with an idempotent sed that appends
/clang:-msse4.1
/clang:-mssse3
/clang:-msse3
/clang:-msse2
right before the closing paren of the COMPILE_FLAGS setter. The patch
is marked with a WZP_SSE_PATCH comment so re-runs skip it.
Confirmed the error message matches with/without the env var — same
20 clang errors from NSQ_del_dec_sse4_1.c / NSQ_sse4_1.c before and
after 990b6f1, which is how we ruled out the env-var path.
fa042b130c