gummiboot 11-2 is not built with $RPM_OPT_FLAGS and its -debuginfo package is empty.
gummiboot.efi is a PE EFI binary which only runs inside an EFI firmware, not on a normal Linux host. We cannot add the normal Linux OPT_FLAGS, it's a very specific requirement to build Windows-like PE executables. For the same reason, we have no useful debug information to extract or provide. I've disabled the creation of the debuginfo package now. Thanks!