Error: Fix build when qemu-common.h is not included

Commit e4ea5e2d0e added the use of
the macro GCC_FMT_ATTR to error.h, however compiler.h is not
included by error.h

This will cause a build error when files including error.h
don't include qemu-common.h (or compiler.h). Not an issue today
because the only file including it is json-parser.h and it does
include qemu-common.h, but let's get it fixed.

Signed-off-by: Luiz Capitulino <lcapitulino@gmail.com>

error.h

@@ -12,6 +12,7 @@
 #ifndef ERROR_H
 #define ERROR_H
 
+#include "compiler.h"
 #include <stdbool.h>
 
 /**