fix trivial warnings

mainly unused parameter and unused function
some parameters are indeed used in a debug built, I used the
(void)(param) trick
warnings reported by clang 4

code/glTFImporter.cpp

@@ -154,7 +154,7 @@ static void CopyValue(const glTF::mat4& v, aiMatrix4x4& o)
     o.a4 = v[12]; o.b4 = v[13]; o.c4 = v[14]; o.d4 = v[15];
 }
 
-inline void SetMaterialColorProperty(std::vector<int>& embeddedTexIdxs, Asset& r, glTF::TexProperty prop, aiMaterial* mat,
+inline void SetMaterialColorProperty(std::vector<int>& embeddedTexIdxs, Asset& /*r*/, glTF::TexProperty prop, aiMaterial* mat,
     aiTextureType texType, const char* pKey, unsigned int type, unsigned int idx)
 {
     if (prop.texture) {
@@ -234,6 +234,7 @@ static inline void SetFace(aiFace& face, int a, int b, int c)
     face.mIndices[2] = c;
 }
 
+#ifdef ASSIMP_BUILD_DEBUG
 static inline bool CheckValidFacesIndices(aiFace* faces, unsigned nFaces, unsigned nVerts)
 {
     for (unsigned i = 0; i < nFaces; ++i) {
@@ -245,6 +246,7 @@ static inline bool CheckValidFacesIndices(aiFace* faces, unsigned nFaces, unsign
     }
     return true;
 }
+#endif // ASSIMP_BUILD_DEBUG
 
 void glTFImporter::ImportMeshes(glTF::Asset& r)
 {