AArch64: Add command line option to select big or little endian

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@205966 91177308-0d34-0410-b5e6-96231b3b80d8
ARM: Add command line option to select big or little endian

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@205967 91177308-0d34-0410-b5e6-96231b3b80d8