[Support] Update comments about stdout, raw_fd_ostream, and outs()
The full story is in the comments:
// Do not attempt to close stdout or stderr. We used to try to maintain the
// property that tools that support writing file to stdout should not also
// write informational output to stdout, but in practice we were never able to
// maintain this invariant. Many features have been added to LLVM and clang
// (-fdump-record-layouts, optimization remarks, etc) that print to stdout, so
// users must simply be aware that mixed output and remarks is a possibility.
NFC, I am just updating comments to reflect reality.
llvm-svn: 310016