test/Modules/compiler_builtins.m: Appease Cygwin to add -D__need_wint_t.
test/Modules/compiler_builtins.m: Appease Cygwin to add -D__need_wint_t.

On Cygwin, at first, <stddef.h> is included without __need_wint_t.
Next, <stddef.h> is included with __need_wint_t, though Modules feature would not process <stddef.h> twice.
Then, wint_t is not found in system headers.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@149500 91177308-0d34-0410-b5e6-96231b3b80d8

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