Support a quieter bp2build

Tie verbosity of bp2build to env var BP2BUILD_VERBOSE

Test: m bp2build
Test: BP2BUILD_VERBOSE=true m bp2build
Change-Id: Ib8f10ad73ed06c935126a77d18c1d9febc25348f
diff --git a/cmd/soong_build/main.go b/cmd/soong_build/main.go
index dfc4eae..c81d4bc 100644
--- a/cmd/soong_build/main.go
+++ b/cmd/soong_build/main.go
@@ -386,7 +386,7 @@
 // - won't be overwritten by corresponding bp2build generated files
 //
 // And return their paths so they can be left out of the Bazel workspace dir (i.e. ignored)
-func getPathsToIgnoredBuildFiles(topDir string, generatedRoot string, srcDirBazelFiles []string) []string {
+func getPathsToIgnoredBuildFiles(topDir string, generatedRoot string, srcDirBazelFiles []string, verbose bool) []string {
 	paths := make([]string, 0)
 
 	for _, srcDirBazelFileRelativePath := range srcDirBazelFiles {
@@ -416,7 +416,9 @@
 			// BUILD file clash resolution happens later in the symlink forest creation
 			continue
 		}
-		fmt.Fprintf(os.Stderr, "Ignoring existing BUILD file: %s\n", srcDirBazelFileRelativePath)
+		if verbose {
+			fmt.Fprintf(os.Stderr, "Ignoring existing BUILD file: %s\n", srcDirBazelFileRelativePath)
+		}
 		paths = append(paths, srcDirBazelFileRelativePath)
 	}
 
@@ -523,7 +525,7 @@
 		os.Exit(1)
 	}
 
-	pathsToIgnoredBuildFiles := getPathsToIgnoredBuildFiles(topDir, generatedRoot, existingBazelRelatedFiles)
+	pathsToIgnoredBuildFiles := getPathsToIgnoredBuildFiles(topDir, generatedRoot, existingBazelRelatedFiles, configuration.IsEnvTrue("BP2BUILD_VERBOSE"))
 	excludes = append(excludes, pathsToIgnoredBuildFiles...)
 
 	excludes = append(excludes, getTemporaryExcludes()...)