stb_image: Avoid stdint.h on 32-bit Symbian.

As suggested by "mupfdev" on Github. We don't have a way to test
here but seems simple enough.

Fixes issue #1321.

stb_image.h

@@ -635,7 +635,7 @@ STBIDEF int   stbi_zlib_decode_noheader_buffer(char *obuffer, int olen, const ch
    #endif
 #endif
 
-#ifdef _MSC_VER
+#if defined(_MSC_VER) || defined(__SYMBIAN32__)
 typedef unsigned short stbi__uint16;
 typedef   signed short stbi__int16;
 typedef unsigned int   stbi__uint32;