Add build_* meta files to allowlist in Dangling rules check

Both `m` and `m --soong-only` generates these files from soong_ui and
not from the primary ninja execution. build/make/core/main.mk then
creates an empty rule to prevent the dangling rule check.

In preparation for turning on "test for dangling rules" in m
--soong-only, add these files to the allowlist

Test: m checkbuild --soong-only
Bug: 394096939
Change-Id: Id702e5753c9892f87e3cf043e51ed86fb5a33862
diff --git a/ui/build/test_build.go b/ui/build/test_build.go
index 7a2fd16..87bec93 100644
--- a/ui/build/test_build.go
+++ b/ui/build/test_build.go
@@ -76,8 +76,10 @@
 	// treated as an source file.
 	dexpreoptConfigFilePath := filepath.Join(outDir, "soong", "dexpreopt.config")
 
-	// out/build_date.txt is considered a "source file"
+	// out/build_(date|hostname|number).txt is considered a "source file"
 	buildDatetimeFilePath := filepath.Join(outDir, "build_date.txt")
+	buildHostnameFilePath := filepath.Join(outDir, "soong", "build_hostname.txt")
+	buildNumberFilePath := filepath.Join(outDir, "soong", "build_number.txt")
 
 	// release-config files are generated from the initial lunch or Kati phase
 	// before running soong and ninja.
@@ -102,6 +104,8 @@
 			line == extraVariablesFilePath ||
 			line == dexpreoptConfigFilePath ||
 			line == buildDatetimeFilePath ||
+			line == buildHostnameFilePath ||
+			line == buildNumberFilePath ||
 			strings.HasPrefix(line, releaseConfigDir) ||
 			buildFingerPrintFilePattern.MatchString(line) {
 			// Leaf node is in one of Soong's bootstrap directories, which do not have