Teach the interpreter to read and write memory in the

Teach the interpreter to read and write memory in the
endianness of the target not of the host.  Done by the
simple expedient of reversing bytes for primitive types
if the host and target endianness don't match.  This is
correct for integer and pointer types.  I don't know if
it is correct for floating point types.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45039 91177308-0d34-0410-b5e6-96231b3b80d8