The native tablegen/tools sub-build (CROSS_TOOLCHAIN_FLAGS_NATIVE) generated
native.cmake against $COOKBOOK_TOOLCHAIN (the Redox cross sysroot) and never
cleared the inherited cross CMAKE_*_FLAGS, so the host try_compile linked
relibc and died with 'undefined reference to __libc_start_main'. Port llvm21's
proven fix: save+unset LDFLAGS/CFLAGS/CXXFLAGS, generate native.cmake against
/usr, CACHE FORCE-clear the cross flags for the native sub-cache, and restore
the cross flags via -DCMAKE_*_FLAGS (not the environment) for the cross build.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
vasilito
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