Make bgplob an exception to dangling rule check.

It's built explicitly by Microfactory but is under out/ and as such, it
would be normally flagged as a file in out/ that doesn't have a
generating rule.

Previously, a no-op rule was added to the Ninja file to prevent this
from happening, but there is no good reason to have two mechanisms to
exempt files under out/ from that check.

Test: Presubmits.
Change-Id: I37fc458ecc5f5734cd81bce2f4894063658df38f
diff --git a/ui/build/test_build.go b/ui/build/test_build.go
index 83007be..86c8568 100644
--- a/ui/build/test_build.go
+++ b/ui/build/test_build.go
@@ -76,6 +76,9 @@
 	// out/build_date.txt is considered a "source file"
 	buildDatetimeFilePath := filepath.Join(outDir, "build_date.txt")
 
+	// bpglob is built explicitly using Microfactory
+	bpglob := filepath.Join(config.SoongOutDir(), "bpglob")
+
 	danglingRules := make(map[string]bool)
 
 	scanner := bufio.NewScanner(stdout)
@@ -88,7 +91,8 @@
 		if strings.HasPrefix(line, modulePathsDir) ||
 			line == variablesFilePath ||
 			line == dexpreoptConfigFilePath ||
-			line == buildDatetimeFilePath {
+			line == buildDatetimeFilePath ||
+			line == bpglob {
 			// Leaf node is in one of Soong's bootstrap directories, which do not have
 			// full build rules in the primary build.ninja file.
 			continue