Turn on ninja error for missing dep files

So that ninja produces an error instead of just a warning when a dep
file is not produced.

Bug: 121058584
Test: check build logs for "depfile is missing" warning
Test: treehugger
Change-Id: I1cbaba866eaf293495c3c0b2b174190bcb2b0f9a

ui/build/ninja.go

@@ -54,7 +54,9 @@ func runNinja(ctx Context, config Config) {
 
 	args = append(args, "-f", config.CombinedNinjaFile())
 
-	args = append(args, "-w", "dupbuild=err")
+	args = append(args,
+		"-w", "dupbuild=err",
+		"-w", "missingdepfile=err")
 
 	cmd := Command(ctx, config, "ninja", executable, args...)
 	if config.HasKatiSuffix() {