bfd/ld: handle ABI prefixes in version scripts

The default language in version scripts is supposed to be C, but no
symbol demangling is performed on the symbols by default.  This makes
targets with a symbol prefix to fail with most version scripts out
there.  So strip away this prefix by default.

This fixes many tests (real world and ld's testsuite) for Blackfin
targets and doesn't seem to cause regressions for x86_64.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>