[mips][mcjit] Add support for R_MIPS_PC32.

Summary:
This allows us to resolve relocations for DW_EH_PE_pcrel TType encodings
in the exception handling LSDA.

Also fixed a nearby typo.

Reviewers: petarj, vkalintiris

Reviewed By: vkalintiris

Subscribers: vkalintiris, llvm-commits

Differential Revision: http://reviews.llvm.org/D10127

llvm-svn: 238844