Disallow __DATE__/__TIME__ on host builds

Instead of just making this an error when building for the device, also
turn on this error for host builds. This is more important as we begin
to use remote caches during the build.

Test: treehugger
Change-Id: I6fcc945464032d951729aead540ea77850c88c41

cc/config/global.go

@@ -46,6 +46,8 @@ var (
 		"-g",
 
 		"-fno-strict-aliasing",
+
+		"-Werror=date-time",
 	}
 
 	commonGlobalConlyflags = []string{}
@@ -67,7 +69,6 @@ var (
 		"-Werror=non-virtual-dtor",
 		"-Werror=address",
 		"-Werror=sequence-point",
-		"-Werror=date-time",
 		"-Werror=format-security",
 	}