[mips64] Fix MIPS64 exception personality encoding

Remove dynamic relocations of __gxx_personality_v0 from the .eh_frame.
The MIPS64 follow-up of the MIPS32 fix (rL209907).

Patch by Vladimir Stefanovic.

Differential Revision: http://reviews.llvm.org/D6141


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221408 91177308-0d34-0410-b5e6-96231b3b80d8