compiler-rt not appending -target <triple> to CFLAGS when cross compiling

Hi,

My cross compile to AArch64 is failing when compiling
compiler-rt/lib/asan/asan_interceptors_vfork.S because the -target
<triple> is not added to the clang command. When that tag is added to
the compilation command, it succeeds. Am I missing something, or is
this a bug? Thanks.