configure: fix configure when using gcc

Fixes Ticket4922.

Commit 060102389e broke configure, since
the inversion ! was missed while converting the grep to a case
statement.

Reviewed-by: Nicolas George <george@nsup.org>
Reviewed-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>

configure

@@ -3621,7 +3621,8 @@ probe_cc(){
         gcc_ext_ver=$(expr "$gcc_version" : ".*$gcc_pkg_ver $gcc_basever \\(.*\\)")
         _ident=$(cleanws "gcc $gcc_basever $gcc_pkg_ver $gcc_ext_ver")
         case $gcc_basever in
-            2*) _depflags='-MMD -MF $(@:.o=.d) -MT $@' ;;
+            2*) ;;
+            *) _depflags='-MMD -MF $(@:.o=.d) -MT $@' ;;
         esac
         if [ "$first" = true ]; then
             case $gcc_basever in