True auto type detection

[rhysd]

Currently libclang-vim handles type deduction by itself here. But true type deduction in libclang has already been supported and we should use it.

[vmiklos]

FWIW, when not hacking on libclang-vim itself, I use libclang-vim with clang-3.7 provided by my distro. That doesn't have the fix yet. So I'm happy with the current situation till distros in general stop shipping broken clang. ;-)

[rhysd]

That makes sense :). The bug looks to be fixed in r246778. The fix was submitted Sep 2015 and Clang 3.7 was released Aug 2015. So clang_getCanonicalType with auto type declaration should work fine in Clang 3.8. I think the best way is switching implementation by Clang version. 3.7 or earlier use current implementation and 3.8 or later use clang_getCanonicalType assuming it can obtain the actual type of auto declaration.

[rhysd]

I found CXVersion. I think we can switch implementation by looking at it.

http://clang.llvm.org/doxygen/structCXVersion.html