Support __decltype() as a synonym for decltype() for gcc compatibility

[llvmbot]

Bugzilla Link	9585
Resolution	FIXED
Resolved on	Apr 04, 2011 02:20
Version	trunk
OS	All
Blocks	#9955
Reporter	LLVM Bugzilla Contributor
CC	@chandlerc,@DougGregor,@efriedma-quic

Extended Description

$ cat test2.cc
#include
$ ./clang++ -nostdinc++ -isystem /opt/local/include/gcc46/c++/ -isystem /opt/local/include/gcc46/c++/x86_64-apple-darwin10/ -c test2.cc
...
/opt/local/include/gcc46/c++/bits/stl_algobase.h:731:32: error: expected ';' in 'for' statement specifier
for (__decltype(__n + 0) __niter = __n;
^
...
20 errors generated.
$ g++-mp-4.6 -c test2.cc
$

Note that this is not compiling in C++0x mode.

__decltype only appears twice in libstdc++-4.6.0, so arguably we should just get gcc to remove it for 4.6.1, but if clang can support it directly that'll make it easier for early adopters.

[llvmbot]

I tried to fix this in libstdc++, but gcc rejects decltype in C++98 mode even in system headers, while it allows __decltype everywhere.

[efriedma-quic]

It's a one-line change; not worth trying to get libstdc++ changed over it. r128809.