clang-cl.exe -fmacro-backtrace-limit=0

It is a bit unfortunate that the clang-cl.exe wrapper can emit diagnostics containing "note: (skipping 5 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)" but invoking clang-cl.exe with that argument fails hard with "clang-cl.exe: error: unknown argument; '-fmacro-backtrace-limit=0'". But it is not obvious to me what would need patching to support that argument in cl mode.

Should be fixed by r234684.

- Hans