Applying: x86_64: Conditionally define __sfp_handle_exceptions for compiler-rt
Applying: configure: Parametrize runtime libraries to support compiler-rt
Applying: configure: Repurpose have-cc-with-libunwind for clang support
Applying: nptl: Only issues __libc_unwind_link_get for SHARED
Applying: Support loading libunwind instead of libgcc_s