PATCH: fix __func__ for C++ destructors

[Matt Austern <austern at apple dot com>]

As discussed earlier on gcc@gcc.gnu.org: __func__ returns a short 
string, without scope or type information, containing the name of the 
current function.  Inside a C++ destructor foo::~foo(), it returns 
"foo", not "~foo".  Users consider this a bug.  I have to agree.  It's 
counterintuitive, and nothing in our documentation suggests that it 
should do this.

(Note that this is a GNU extension.  __func__ is part of standard C, 
but not standard C++.)

The problem is in c-common.c, in fname_as_string.  It thinks that the 
contents of DECL_NAME is an acceptable human-readable string.  
Sometimes that assumption is right, sometimes it isn't.  The right way 
to get a short human-readable string is to use 
*lang_hooks.decl_printable_name with verbosity 0.

This patch does that.  ChangeLog entries and three new test cases are 
included.  I've verified that the patch doesn't break the bootstrap, 
and that it's only impact on test status is that it makes one of my new 
tests succeed where it used to fail.

OK to commit to mainline?

			--Matt

P.S.  Just out of curiosity, I also checked the behavior of even more 
esoteric C++ member functions.  A user-defined conversion operator that 
shows up as "operator Pv" before my patch shows up as "operator void*" 
afterwards.  I think this is an improvement.  I also think it's too 
esoteric to be worth writing a fourth test case for.

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