vertexcodec: Fix typedef shadowing warning in amalgamated builds

We define unaligned_int in meshopt:: namespace in meshletcodec.cpp and
inside decodeBytesGroupSimd in vertexcodec.cpp. These definitions do not
conflict but produce Wshadow warning on clang.

Since they are identical, we can move the vertexcodec definition to
meshopt namespace too; this results in typedef redefinition which is
valid when it's redundant (the type is the same).

Author: zeux

src/vertexcodec.cpp

@@ -816,6 +816,12 @@ inline __m128i decodeShuffleMask(unsigned char mask0, unsigned char mask1)
 	return _mm_unpacklo_epi64(sm0, sm1r);
 }
 
+#ifdef __GNUC__
+typedef int __attribute__((aligned(1))) unaligned_int;
+#else
+typedef int unaligned_int;
+#endif
+
 SIMD_TARGET
 inline const unsigned char* decodeBytesGroupSimd(const unsigned char* data, unsigned char* buffer, int hbits)
 {
@@ -834,12 +840,6 @@ inline const unsigned char* decodeBytesGroupSimd(const unsigned char* data, unsi
 	case 1:
 	case 6:
 	{
-#ifdef __GNUC__
-		typedef int __attribute__((aligned(1))) unaligned_int;
-#else
-		typedef int unaligned_int;
-#endif
-
 #ifdef SIMD_LATENCYOPT
 		unsigned int data32;
 		memcpy(&data32, data, 4);