Ignore llvm specific symbols in the LTOModule.

These are the llvm.* globals and functions.

I don't think it is possible to test this directly since llvm-lto is not
a full linker and will not report duplicated symbols, but this fixes
bootstrap with gold and lto enabled.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212354 91177308-0d34-0410-b5e6-96231b3b80d8