We build libc++ and libc++abi with -nostdlib,defaultlibs, so -rtlib=compiler-rt has no
effect and results in an 'argument unused during compilation' warning which
breaks the build when using -Werror. so this is not neededWe can therefore drop -rtlib=compiler-rt
and results in 'argument unused duringwithout any functional change; note that the actual compilation' warner-rt linking whichis
breaks the build when using -Werrorhandled by HandleCompilerRT.