Need BuildRequires: gcc

[tonyhutter]

System information

Type	Version/Name
Distribution Name	Fedora
Distribution Version	29
Linux Kernel	-
Architecture	-
ZFS Version	master
SPL Version	master

Describe the problem you're observing

The Fedora 29 mock environment no longer includes GCC by default:
https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/thread/TDPFN4KWRZNGGLS4PGWDRFHRKFLVOHXA/

We should add a BuildRequires: gcc into our spec files. This has been a packaging requirement for awhile now:

If your application is a C or C++ application you must list a BuildRequires against gcc, gcc-c++ or clang. Those packages will include everything that is required to build a standards conforming C or C++ application.

https://fedoraproject.org/wiki/Packaging:C_and_C%2B%2B

Describe how to reproduce the problem

Build zfs-0.7.12-hutter (#8078) in a F29 mock environment.

Include any warning/errors/backtraces from the system logs