[Bug bootstrap/18532] libgcc.mk isn't parallel build safe for multilib

[hjl at lucon dot org]

-- 
Bug 18532 depends on bug 18533, which changed state.

Bug 18533 Summary: EXTRA_MULTILIB_PARTS are used to build libgcc_s.so for 
multilib
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18533

           What    |Old Value                   |New Value
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18532