Stop first pass of mixed bazel builds before writing ninja

This shaves off ~20s, which is ~11%, of `m nothing` with mixed builds.

Test: Manual verification with mixed builds of aosp_flame.
Change-Id: Ief1bc56c92329e899c829fc1374eea9ee9b94fb7
diff --git a/cmd/soong_build/main.go b/cmd/soong_build/main.go
index 9d7dddd..fe413f3 100644
--- a/cmd/soong_build/main.go
+++ b/cmd/soong_build/main.go
@@ -95,6 +95,7 @@
 		// TODO(cparsons): Don't output any ninja file, as the second pass will overwrite
 		// the incorrect results from the first pass, and file I/O is expensive.
 		firstCtx := newContext(srcDir, configuration)
+		configuration.SetStopBefore(bootstrap.StopBeforeWriteNinja)
 		bootstrap.Main(firstCtx.Context, configuration, extraNinjaDeps...)
 		// Invoke bazel commands and save results for second pass.
 		if err := configuration.BazelContext.InvokeBazel(); err != nil {