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/demux.c

@@ -22,6 +22,7 @@
 #include <stdint.h>
 
 #include "config.h"
+#include "config_components.h"
 
 #include "libavutil/avassert.h"
 #include "libavutil/avstring.h"