Generate vendor specific STUB_LIBRARIES

When generating vendor/etc/linker.config.pb, STUB_LIBRARIES was used.
Because it lists *all* libraries with stubs regardless of its
install location (vendor or system), using it for vendor
linker.config.pb doesn't make sense. Instead, use vendor-specific
STUB_LIBRARIES, which is named SOONG_STUB_VENDOR_LIBRARIES.

Bug: 313806237
Test: m (aosp_cf_x86_64_phone)
Test: $OUT/vendor/etc/linker.config.pb not listing libz.so
Change-Id: Icd0aaf92d9630c07f58c4739a9f0ac713516db43
diff --git a/cc/stub_library.go b/cc/stub_library.go
index 3a6d0ae..47c6cb9 100644
--- a/cc/stub_library.go
+++ b/cc/stub_library.go
@@ -27,7 +27,8 @@
 }
 
 type stubLibraries struct {
-	stubLibraryMap map[string]bool
+	stubLibraryMap       map[string]bool
+	stubVendorLibraryMap map[string]bool
 
 	apiListCoverageXmlPaths []string
 }
@@ -54,6 +55,9 @@
 			if IsStubTarget(m) {
 				if name := getInstalledFileName(m); name != "" {
 					s.stubLibraryMap[name] = true
+					if m.InVendor() {
+						s.stubVendorLibraryMap[name] = true
+					}
 				}
 			}
 			if m.library != nil {
@@ -67,13 +71,15 @@
 
 func stubLibrariesSingleton() android.Singleton {
 	return &stubLibraries{
-		stubLibraryMap: make(map[string]bool),
+		stubLibraryMap:       make(map[string]bool),
+		stubVendorLibraryMap: make(map[string]bool),
 	}
 }
 
 func (s *stubLibraries) MakeVars(ctx android.MakeVarsContext) {
 	// Convert stub library file names into Makefile variable.
 	ctx.Strict("STUB_LIBRARIES", strings.Join(android.SortedKeys(s.stubLibraryMap), " "))
+	ctx.Strict("SOONG_STUB_VENDOR_LIBRARIES", strings.Join(android.SortedKeys(s.stubVendorLibraryMap), " "))
 
 	// Export the list of API XML files to Make.
 	sort.Strings(s.apiListCoverageXmlPaths)