[JIT] Fix more missing endian conversions (opcodes for AArch64, ARM, and Mips stub functions, and ARM target in general)

Summary:
Fixed all of the missing endian conversions that Lang Hames and I identified in
RuntimeDyldMachOARM.h.

Fixed the opcode emission in RuntimeDyldImpl::createStubFunction() for AArch64,
ARM, Mips when the host endian doesn't match the target endian.
PowerPC will need changing if it's opcodes are affected by endianness but I've
left this for now since I'm unsure if this is the case and it's the only path
that specifies the target endian.

This patch fixes MachO_ARM_PIC_relocations.s on a big-endian Mips host. This
is the last of the known issues on this host.

Reviewers: lhames

Reviewed By: lhames

Subscribers: aemerson, llvm-commits

Differential Revision: http://reviews.llvm.org/D6130