gcc: Refactor linker patches and fix linker on arm with usrmerge

Backport fix from master to allow gcc to use proper linker path for
musl [Yocto #14977].

Fixes:
| qemu-arm: Could not open '/lib/ld-musl-armhf.so.1': No such file or directory

Signed-off-by: Pavel Zhukov <pavel@zhukoff.net>
Signed-off-by: Steve Sakoman <steve@sakoman.com>