Add BuildRequires gcc, make, elfutils-libelf-devel

This adds a BuildRequires for gcc, make, and elfutils-libelf-devel
into our spec files.  gcc has been a packaging requirement for
awhile now:

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

These additional BuildRequires allow us to mock build in
Fedora 29.

Reviewed-by: Neal Gompa <ngompa@datto.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by:  Tony Hutter <hutter2@llnl.gov>
Closes #8095
Closes #8102

rpm/generic/zfs-kmod.spec.in

@@ -52,6 +52,10 @@ URL:            http://zfsonlinux.org/
 Source0:        %{module}-%{version}.tar.gz
 Source10:       kmodtool
 BuildRoot:      %{_tmppath}/%{name}-%{version}-%{release}-root-%(%{__id} -u -n)
+%if 0%{?rhel}%{?fedora}
+BuildRequires:  gcc, make
+BuildRequires:  elfutils-libelf-devel
+%endif
 
 # The developments headers will conflict with the dkms packages.
 Conflicts:      %{module}-dkms

rpm/generic/zfs.spec.in

@@ -91,6 +91,7 @@ Provides:       %{name}-kmod-common = %{version}
 Conflicts:      zfs-fuse
 
 %if 0%{?rhel}%{?fedora}%{?suse_version}
+BuildRequires:  gcc, make
 BuildRequires:  zlib-devel
 BuildRequires:  libuuid-devel
 BuildRequires:  libblkid-devel