Support the option -fextended-identifiers

[sylvestre]

Bugzilla Link	11538
Version	unspecified
OS	All
CC	@belkadan,@zygoloid

Extended Description

It would be nice if you could support the option -fextended-identifiers like in gcc/g++:

   -fextended-identifiers
       Accept universal character names in identifiers.  This option is
       experimental; in a future version of GCC, it will be enabled by
       default for C99 and C++.

This wish has been reported on:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=647636

[belkadan]

Supported in C99 and C++ modes as of r173376!

(We don't support it in C89 because it changes parsing a little, but Clang's default C mode is C99 so that shouldn't be a huge issue.)

[zygoloid]

Perhaps we should also support (and ignore) the -fextended-identifiers option?

[belkadan]

For -fextended-identifiers that makes sense. How about -fno-extended-identifiers? We won't honor that, so I'm not sure just swallowing it would make sense.

[belkadan]

Richard, do you have an opinion on -fno-extended-identifiers? I'm not sure whether clang_ignored_f_Group or Unsupported is more correct. (Alternately, we could just add a new LangOpt like Trigraphs that gets set by the language standard.)

[zygoloid]

I'm fine with putting it into Unsupported until/unless someone complains.

[cor3ntin]

Clang supports UAX identifiers in C++ and C2X mode, the flag is supported (and ignored), enabled by default in C99+ by gcc.
This issue no longer seems relevant.