Add code to enable USE_BAZEL=1 m functionality in AOSP.

Test: Manually, but builds currently fail due to a recent change to bazel_handler.go.
Change-Id: I9a45a2c73d1755032b11f6b913c03f83a28f63c5

ui/build/build.go

@@ -84,8 +84,10 @@ const (
 	BuildSoong         = 1 << iota
 	BuildKati          = 1 << iota
 	BuildNinja         = 1 << iota
+	BuildBazel         = 1 << iota
 	RunBuildTests      = 1 << iota
 	BuildAll           = BuildProductConfig | BuildSoong | BuildKati | BuildNinja
+	BuildAllWithBazel  = BuildProductConfig | BuildSoong | BuildKati | BuildBazel
 )
 
 func checkProblematicFiles(ctx Context) {
@@ -257,6 +259,10 @@ func Build(ctx Context, config Config, what int) {
 		// Run ninja
 		runNinja(ctx, config)
 	}
+
+	if what&BuildBazel != 0 {
+		runBazel(ctx, config)
+	}
 }
 
 // distGzipFile writes a compressed copy of src to the distDir if dist is enabled.  Failures