Don't allow a lib having stubs to become a member of VNDK

If a lib has stubs, that means the library provides stable C APIs and
the APIs are guaranteed to be maintained in a backwards compatible
manner. Then there is no reason to have the same library in VNDK,
because VNDK is for libraries (usually having C++ interfaces) where API
stability across the yearly releases is hard (or impossible) to be
guaranteed.

This change triggers an error when the build system finds a VNDK lib
which has stubs defined. Users are suggested to make the lib an LLNDK
one.

Bug: 151303316
Test: m
Change-Id: Id305196a9d5a6fc7e7f9c02f3fa076859dc9a282

cc/vndk.go

@@ -309,6 +309,10 @@ func processVndkLibrary(mctx android.BottomUpMutatorContext, m *Module) {
 		panic(err)
 	}
 
+	if m.HasStubsVariants() {
+		mctx.PropertyErrorf("vndk.enabled", "This library provides stubs. Shouldn't be VNDK. Consider making it as LLNDK")
+	}
+
 	vndkLibrariesLock.Lock()
 	defer vndkLibrariesLock.Unlock()