Make llvmc work again.

Chris recently broke llvmc with his Makefile changes (r75379). That patch made
the global change .o -> .a, which caused built-in llvmc plugins to stop working
since plugin initialization in llvmc is based on static variables not referenced
from the main executable. This patch implements auto-generated forced references
to the plugin libraries.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@74000 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed