[Bug c/67224] UTF-8 support for identifier names in GCC

["joseph at codesourcery dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67224

--- Comment #11 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
Sorry, glibc iconv (not libiconv) doesn't handle "C99".  So your patch 
would not work on any GNU host in normal configurations of GCC (libiconv 
is a completely separate package and is only likely to be used on non-GNU 
hosts such as Windows, on GNU hosts iconv from glibc is normally used 
although it's possible to use libiconv there).

You need to test cases such as that if a macro is defined twice, once with 
a UCN in its expansion and once with the equivalent character written in 
UTF-8, the difference in the expansion is diagnosed (whichever of all the 
valid UCNs for that character is the one used).  And that the original 
spelling appears on the right hand side of a definition output with -dD.  
And that if (in C but not, properly, C++) a string contains a backslash 
followed by an extended character, this is properly diagnosed as an 
invalid escape sequence rather than being treated as \\u<something> or 
\\U<something>.  See the tests in my spelling preservation patch 
<https://gcc.gnu.org/ml/gcc-patches/2014-11/msg00548.html>.  (Stringizing 
isn't necessarily an issue here because of the special C rules about 
stringizing UCNs together with the C++ rule about converting to UCNs in 
phase 1 - the effect is that for C it's always OK to stringize as the 
extended character, though you can't stringize as a UCN if the extended 
character was originally written, while for C++ you have to stringize as a 
UCN.)  And then you need tests of C++ programs with extended characters 
inside raw strings (like c-c++-common/raw-string-*.c, but none of those 
cover extended characters at present).  And the patch needs to add all 
these tests to the testsuite.