[Mips] Make exe-got.test test case independent from external input files.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@210977 91177308-0d34-0410-b5e6-96231b3b80d8
Using llvm::sys::swapByteOrder() for the common case of byte-swapping a value in place

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@210979 91177308-0d34-0410-b5e6-96231b3b80d8