Add --multitree-build flag

Add a flag that enables logic specific to multitree-build builds.

Bug: b/266730267
Test: treehugger, manual
Change-Id: Ia6f392525faa9d66bb6e0692b2a2e9c3b8493b0d
diff --git a/android/config.go b/android/config.go
index 979f1ca..292fcf2 100644
--- a/android/config.go
+++ b/android/config.go
@@ -83,6 +83,8 @@
 	ModuleActionsFile   string
 	DocFile             string
 
+	MultitreeBuild bool
+
 	BazelMode                bool
 	BazelModeDev             bool
 	BazelModeStaging         bool
@@ -229,6 +231,10 @@
 	Bp2buildPackageConfig          Bp2BuildConversionAllowlist
 	Bp2buildSoongConfigDefinitions soongconfig.Bp2BuildSoongConfigDefinitions
 
+	// If MultitreeBuild is true then this is one inner tree of a multitree
+	// build directed by the multitree orchestrator.
+	MultitreeBuild bool
+
 	// If testAllowNonExistentPaths is true then PathForSource and PathForModuleSrc won't error
 	// in tests when a path doesn't exist.
 	TestAllowNonExistentPaths bool
@@ -449,7 +455,8 @@
 		mixedBuildEnabledModules:  make(map[string]struct{}),
 		bazelForceEnabledModules:  make(map[string]struct{}),
 
-		UseBazelProxy: cmdArgs.UseBazelProxy,
+		MultitreeBuild: cmdArgs.MultitreeBuild,
+		UseBazelProxy:  cmdArgs.UseBazelProxy,
 	}
 
 	config.deviceConfig = &deviceConfig{