PR26087: Use nonstandard MSVC extension for VS2015 as well.

In r256564, I had conditioned the workaround in has_getDecl to only be
used for MSVC before the 2015 release, believing that 2015 could handle
the standard code. But, that was incorrect.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@257392 91177308-0d34-0410-b5e6-96231b3b80d8