Mixed bazel/soong build prototype for genrule

With this change, bazel_module is a specifiable property on
genrule module definitions. With bazel-enabled mode, soong_build will
defer to Bazel for information on these modules.

source build/soong/bazelenv.sh to enter bazel-enabled mode.

Test: Manually verified on bionic/libc genrules using aosp_cf_x86_phone-userdebug
Change-Id: I3619848186d50be7273a5eba31c79989b981d408

android/config.go

@@ -85,6 +85,8 @@ type config struct {
 	// Only available on configs created by TestConfig
 	TestProductVariables *productVariables
 
+	BazelContext BazelContext
+
 	PrimaryBuilder           string
 	ConfigFileName           string
 	ProductVariablesFileName string
@@ -248,6 +250,8 @@ func TestConfig(buildDir string, env map[string]string, bp string, fs map[string
 		// Set testAllowNonExistentPaths so that test contexts don't need to specify every path
 		// passed to PathForSource or PathForModuleSrc.
 		testAllowNonExistentPaths: true,
+
+		BazelContext: noopBazelContext{},
 	}
 	config.deviceConfig = &deviceConfig{
 		config: config,
@@ -324,6 +328,20 @@ func TestArchConfig(buildDir string, env map[string]string, bp string, fs map[st
 	return testConfig
 }
 
+// Returns a config object which is "reset" for another bootstrap run.
+// Only per-run data is reset. Data which needs to persist across multiple
+// runs in the same program execution is carried over (such as Bazel context
+// or environment deps).
+func ConfigForAdditionalRun(c Config) (Config, error) {
+	newConfig, err := NewConfig(c.srcDir, c.buildDir, c.moduleListFile)
+	if err != nil {
+		return Config{}, err
+	}
+	newConfig.BazelContext = c.BazelContext
+	newConfig.envDeps = c.envDeps
+	return newConfig, nil
+}
+
 // New creates a new Config object.  The srcDir argument specifies the path to
 // the root source directory. It also loads the config file, if found.
 func NewConfig(srcDir, buildDir string, moduleListFile string) (Config, error) {
@@ -425,6 +443,10 @@ func NewConfig(srcDir, buildDir string, moduleListFile string) (Config, error) {
 		Bool(config.productVariables.GcovCoverage) ||
 			Bool(config.productVariables.ClangCoverage))
 
+	config.BazelContext, err = NewBazelContext(config)
+	if err != nil {
+		return Config{}, err
+	}
 	return Config{config}, nil
 }