Use the avstring.h locale-independent character type functions

Make sure the behavior does not change with the locale.

Signed-off-by: Martin Storsjö <martin@martin.st>

libavcodec/utils.c

@@ -2105,10 +2105,10 @@ int avpriv_unlock_avformat(void)
 
 unsigned int avpriv_toupper4(unsigned int x)
 {
-    return toupper(x & 0xFF)
-           + (toupper((x >> 8) & 0xFF) << 8)
-           + (toupper((x >> 16) & 0xFF) << 16)
-           + (toupper((x >> 24) & 0xFF) << 24);
+    return av_toupper(x & 0xFF) +
+          (av_toupper((x >>  8) & 0xFF) << 8)  +
+          (av_toupper((x >> 16) & 0xFF) << 16) +
+          (av_toupper((x >> 24) & 0xFF) << 24);
 }
 
 #if !HAVE_THREADS