toolchain: Allow ld64.so linker

The glibc dynamic linkers for ppc64 and s390x are named ld64.so.*
so modify the check_glibc test to match them.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Anton Blanchard <anton@samba.org>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>