Random errors and compile flags missing from a chromium build.

[ianamason]

WARNING:Did not recognize the compiler flag: -mbmi
WARNING:Did not recognize the compiler flag: -mbmi2
WARNING:Did not recognize the compiler flag: -mf16c
WARNING:Did not recognize the compiler flag: -mfma
WARNING:Did not recognize the compiler flag: -ggnu-pubnames

gclang++ -Wl,--fatal-warnings -Wl,--build-id=sha1 -fPIC -Wl,-z,noexecstack -Wl,-z,relro -Wl,-z,now -Wl,-z,defs -Wl,--as-needed -fuse-ld=lld -Wl,--icf=all -Wl,--color-diagnostics -flto=thin -Wl,--thinlto-jobs=8 -Wl,--thinlto-cache-dir=thinlto-cache -Wl,--thinlto-cache-policy,cache_size=10\%:cache_size_bytes=10g:cache_size_files=100000 -Wl,--lto-O0 -fwhole-program-vtables -Wl,--no-call-graph-profile-sort -m64 -Wl,-O2 -Wl,--gc-sections -Wl,--gdb-index -rdynamic -fsanitize=cfi-vcall -fsanitize=cfi-icall -pie -Wl,--disable-new-dtags -Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now -o "./brotli" -Wl,--start-group @"./brotli.rsp"  -Wl,--end-group  -latomic -ldl -lpthread -lrt
WARNING:Did not recognize the compiler flag: @./brotli.rsp

clang-10: error: unable to execute command: Segmentation fault (core dumped)
clang-10: error: linker command failed due to signal (use -v to see invocation)
ERROR:Failed to compile using given arguments:
clang++ [-g -Wl,-plugin-opt=save-temps -Wl,--fatal-warnings -Wl,--build-id=sha1 -fPIC -Wl,-z,noexecstack -Wl,-z,relro -Wl,-z,now -Wl,-z,defs -Wl,--as-needed -fuse-ld=lld -Wl,--icf=all -Wl,--color-diagnostics -flto=thin -Wl,--thinlto-jobs=8 -Wl,--thinlto-cache-dir=thinlto-cache -Wl,--thinlto-cache-policy,cache_size=10%:cache_size_bytes=10g:cache_size_files=100000 -Wl,--lto-O0 -fwhole-program-vtables -Wl,--no-call-graph-profile-sort -m64 -Wl,-O2 -Wl,--gc-sections -Wl,--gdb-index -rdynamic -fsanitize=cfi-vcall -fsanitize=cfi-icall -pie -Wl,--disable-new-dtags -Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now -o ./brotli -Wl,--start-group @./brotli.rsp -Wl,--end-group -latomic -ldl -lpthread -lrt]