spec: Add explicit gcc build requirement

Signed-off-by: Jan Friesse <jfriesse@redhat.com>

(partly backported afdc4055127b5076e867a516e4a4c4899746a3e8)

corosync.spec.in

@@ -41,6 +41,7 @@ Conflicts: openais <= 0.89, openais-devel <= 0.89
 
 # Build bits
 
+BuildRequires: gcc
 BuildRequires: groff
 BuildRequires: libqb-devel
 BuildRequires: nss-devel