Added standard macro guard. In case __GNUC_VA_LIST was not defined or defined identically before there will not be any change in functionality.
Added standard macro guard. In case __GNUC_VA_LIST was not
defined or defined identically before there will not be any
change in functionality.

MinGW-w64 defines __GNUC_VA_LIST as

  #define __GNUC_VA_LIST
  
which is different than the definition here, causing
a warning without the guard.
 


git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@212183 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang