Musl-libc support

Add explicit support for musl libc (linux-only); the linker information is wrong.

The dynamic loader is named /lib/ld-musl-${ARCH}${SUBARCH}.so.1. E.g.:

/lib/ld-musl-i386.so.1
/lib/ld-musl-x86_64.so.1
/lib/ld-musl-x32.so.1
/lib/ld-musl-armeb.so.1
/lib/ld-musl-armhf.so.1
...

Also, on these systems there might not be multiarch support, or if there is, path would be something like /lib/x86_64-pc-linux-musl, i.e. with the normal gnu suffix replaced by musl.