toolchain: ARM: Fix option conflict with multiarch

toolchain: ARM: Fix option conflict with multiarch

This problem exposed when compiling glibc, but applicable across the
board. gcc compiles runtime libraries for all supported architectures,
unless otherwise specified, and later selects applicable library based
-m[arch,cpu,*] options, thus these options should not be passed to gcc
as they break the compilation process.

Signed-off-by: Boris Krasnovskiy <borkra@gmail.com>
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
[modified so it only touches ARM - I'm too chicken, changed authors email]