Fixed bug where NEON code was #ifdef’d out on GCC/clang even where explicitly requested.

stb_image.h

@@ -624,7 +624,7 @@ typedef unsigned char validate_uint32[sizeof(stbi__uint32)==4 ? 1 : -1];
 #define STBI_FREE(p)       free(p)
 #endif
 
-#if defined(__GNUC__) && !defined(__SSE2__) && !defined(STBI_NO_SIMD)
+#if defined(__GNUC__) && (defined(__x86_64__) || defined(__i386)) && !defined(__SSE2__) && !defined(STBI_NO_SIMD)
 // gcc doesn't support sse2 intrinsics unless you compile with -msse2,
 // (but compiling with -msse2 allows the compiler to use SSE2 everywhere;
 // this is just broken and gcc are jerks for not fixing it properly