Add support for x,y,z,w accessors to fvec4SIMD.

This is done via a union. It must be enabled with GLM_SIMD_ENABLE_XYZW_UNION. A nameless struct/union warning in VC (C4201) is explicitly disabled with the "pragma warning(push/pop)" system.

Allowing xyzw access makes it much easier to toggle between SIMD and non-SIMD builds.

glm/gtx/simd_vec4.hpp

@@ -54,6 +54,14 @@
 #	pragma message("GLM: GLM_GTX_simd_vec4 extension included")
 #endif
 
+
+// Warning silencer for nameless struct/union.
+#if (GLM_COMPILER & GLM_COMPILER_VC)
+#   pragma warning(push)
+#   pragma warning(disable:4201)   // warning C4201: nonstandard extension used : nameless struct/union
+#endif
+
+
 namespace glm{
 namespace detail
 {
@@ -69,7 +77,15 @@ namespace detail
 		typedef fvec4SIMD type;
 		typedef tvec4<bool> bool_type;
 
+#ifdef GLM_SIMD_ENABLE_XYZW_UNION
+        union
+        {
 		    __m128 Data;
+            struct {float x, y, z, w;};
+        };
+#else
+        __m128 Data;
+#endif
 
 		//////////////////////////////////////
 		// Implicit basic constructors
@@ -490,6 +506,12 @@ namespace detail
 
 #include "simd_vec4.inl"
 
+
+#if (GLM_COMPILER & GLM_COMPILER_VC)
+#   pragma warning(pop)
+#endif
+
+
 #endif//(GLM_ARCH != GLM_ARCH_PURE)
 
 #endif//GLM_GTX_simd_vec4