The previous sed-based patch didn't stick in the docker-bash-c
heredoc (bash single-quoting made the newline escaping fragile).
Switch to a much simpler approach: just 'cat >>' a pure-CMake block
to the end of the cargo-xwin toolchain file. The block does:
set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /clang:-msse4.1 ..." CACHE STRING "" FORCE)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /clang:-msse4.1 ..." CACHE STRING "" FORCE)
Running AFTER the toolchain's own FORCE-set and AFTER cmake-rs's
-DCMAKE_C_FLAGS= command-line override, it unconditionally wins. No
sed, no awk, no python, no newline escaping — just CMake reading the
toolchain file like it normally does.
Idempotent via the WZP_SSE_PATCH sentinel grep in the comment block.
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