Fix filamat build (#1005)

Filamat public headers were including a private header. This PR fixes
this problem. It also forces filamat to always be compiled to avoid
breaking filamat without noticing. The flag `-l` is not available
anymore in build.sh as a result.

android/filamat-android/src/main/cpp/MaterialBuilder.cpp

@@ -18,8 +18,6 @@
 
 #include <filamat/MaterialBuilder.h>
 
-#include <private/filament/EngineEnums.h>
-
 using namespace filament;
 using namespace filamat;