Commit e4ea5e2d 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>