[Tests] Add -dump-input fail to environment-mac.swift's FileCheck.

Author: mikeash

test/Driver/environment-mac.swift

@@ -1,5 +1,5 @@
 // REQUIRES: OS=macosx
 
-// RUN: %swift_driver -driver-use-frontend-path %S/Inputs/print-var.sh %s DYLD_LIBRARY_PATH | %FileCheck %s
+// RUN: %swift_driver -driver-use-frontend-path %S/Inputs/print-var.sh %s DYLD_LIBRARY_PATH | %FileCheck %s --dump-input fail
 
 // CHECK: {{^/usr/lib/swift:}}