Untangle headers

Thanks, clang -fmodules.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/backend/backend.h

@@ -5,6 +5,7 @@
 
 #include <stdbool.h>
 
+#include "config.h"
 #include "compiler.h"
 #include "driver.h"
 #include "kernel.h"
@@ -48,14 +49,6 @@ enum image_operations {
 	IMAGE_OP_RESIZE_TILE,
 };
 
-enum blur_method {
-	BLUR_METHOD_NONE = 0,
-	BLUR_METHOD_KERNEL,
-	BLUR_METHOD_BOX,
-	BLUR_METHOD_GAUSSIAN,
-	BLUR_METHOD_INVALID,
-};
-
 struct gaussian_blur_args {
 	int size;
 	double deviation;