toolchain-external: Fix ld.so naming with uClibc and EABIhf.

Currently ld-linux-armhf.so.* is added to external libs when
using an EABIhf toolchain, but this naming is not used by uClibc.
Fix by adding a check for glibc.

Signed-off-by: Stefan Sørensen <stefan.sorensen@spectralink.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>