configure: Use a separate config_components.h header for $ALL_COMPONENTS

This avoids unnecessary rebuilds of most source files if only the
list of enabled components has changed, but not the other properties
of the build, set in config.h.

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

libavformat/au.c

@@ -27,6 +27,8 @@
  * http://www.goice.co.jp/member/mo/formats/au.html
  */
 
+#include "config_components.h"
+
 #include "libavutil/bprint.h"
 #include "avformat.h"
 #include "internal.h"