Disable compilation of llvm-pdbdump for versions of MSVC < 2013.
Disable compilation of llvm-pdbdump for versions of MSVC < 2013.

Certain aspects of llvm-pdbdump require language support only present in
MSVC 2013 and higher.  Since this is strictly a utility, and since we hope
to drop support for MSVC 2012 soon, don't build this unless MSVC 2013 or
higher.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@227479 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,dslab-epfl/asap,dslab-epfl/asap,GPUOpen-Drivers/llvm,apple/swift-llvm,dslab-epfl/asap,apple/swift-llvm,dslab-epfl/asap,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,dslab-epfl/asap,dslab-epfl/asap,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,dslab-epfl/asap,apple/swift-llvm