Remove some std stream usage from Support and TableGen

LLVM's coding standards recommend raw_ostream and MemoryBuffer for
reading and writing text.

This has the side effect of allowing clang to compile more of Support
and TableGen in the Microsoft C++ ABI.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187826 91177308-0d34-0410-b5e6-96231b3b80d8