Re-commit r238838, r238844 with fix for host/target endian mismatch and windows buildbot.

The windows buildbot originally failed because the check expressions are
evaluated as 64-bit values, even for 32-bit symbols. Fixed this by comparing
bottom 32-bits of the expressions.

The host/target endian mismatch issue is that it's invalid to read/write target
values using a host pointer without taking care of endian differences between
the target and host. Most (if not all) instances of
reinterpret_cast<uint32_t*>() in the RuntimeDyld are examples of this bug.
This has been fixed for Mips using the endian aware read/write functions.

The original commits were:
r238838:
[mips] Add RuntimeDyld tests for currently supported O32 relocations.

Reviewers: petarj, vkalintiris

Reviewed By: vkalintiris

Subscribers: vkalintiris, llvm-commits

Differential Revision: http://reviews.llvm.org/D10126

r238844:
[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: 238915