Fix some Wundef warnings in Compiler.h
Fix some Wundef warnings in Compiler.h

Check for definedness of the __cpp_sized_deallocation and
__cpp_aligned_new feature test macros.  These will not be defined
when the feature is not available, and that prevents any code that
includes this header from compiling with -Wundef -Werror.

Differential Revision: https://reviews.llvm.org/D51171


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@341364 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm