[MCJIT] Const-ify the symbol lookup operations on RuntimeDyld.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217263 91177308-0d34-0410-b5e6-96231b3b80d8
Revert "Disable the fix for pr20793 because of a gnu ld bug."

This reverts commit r217211.

Both the bfd ld and gold outputs were valid. They were using a Rela relocation,
so the value present in the relocated location was not used, which caused me
to misread the output.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217264 91177308-0d34-0410-b5e6-96231b3b80d8