Reenable test_buffer on ppc64le

The test failed because of a GCC bug which has been fixed in GCC
master branch and Rawhide uses GCC 9 (master branch):

* https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88892
* https://bugzilla.redhat.com/show_bug.cgi?id=1540995

python38.spec

@@ -989,9 +989,6 @@ CheckPython() {
     %ifarch %{mips64}
     -x test_ctypes \
     %endif
-    %ifarch ppc64le
-    -x test_buffer \
-    %endif
     -x test_asyncio \
 
   echo FINISHED: CHECKING OF PYTHON FOR CONFIGURATION: $ConfName