Also, improve LDBG() to accept debug type and level in any order, and
add unit-tests for LDBG() and LGDB_OS().
LDBG_OS() is a macro that behaves like LDBG() but instead of directly
using it to stream the output, it takes a callback function that will be
called with a raw_ostream.
This is a re-land with workarounds for older gcc and clang versions.
Previous attempts in #157194 and #158260
Co-authored-by: Andrzej Warzyński <andrzej.warzynski@gmail.com>
2832717ecc