Pass --with-tcl to ensure tclConfig.sh is found

On x86_64 the default search path configure uses for tclConfig.sh
does not include /usr/lib64.  The tcl module builds with default
settings, but we can do better by explicitly setting --with-tcl.  This
ensures that TCL_FLAGS is set by tclConfig.sh rather than guessed.

znc.spec

@@ -138,7 +138,7 @@ rm -rf "$gpghome" $key.gpg # Cleanup tmp gpg home dir and dearmored key
 %else # 0%{?with_modpython}
      --disable-python \
 %endif # 0%{?with_modpython}
-     --enable-ipv6 --enable-cyrus --enable-tcl
+     --enable-ipv6 --enable-cyrus --enable-tcl --with-tcl=%{_libdir}
 %make_build V=1
 
 
@@ -222,6 +222,7 @@ getent passwd znc >/dev/null || \
 - Check upstream GPG signature in %%prep
 - Simplify %%{_libdir}/znc/ file list
 - Enable verbose make
+- Pass --with-tcl to ensure tclConfig.sh is found
 
 * Mon Jul 23 2018 Nick Bebout <nb@fedoraproject.org> - 1.7.1-2
 - Add gcc-c++ and redhat-rpm-config to znc-devel's dependencies