Reenable test_gdb on most archs except arm and s390x

gdb has been fixed in Rawhide:
https://bugzilla.redhat.com/show_bug.cgi?id=1638798
https://bugzilla.redhat.com/show_bug.cgi?id=1634781

Install also gdb in selftest to no longer skip test_gdb
on the x86_64 CI.

But test_gdb is still skipped on armv7hl:
https://bugzilla.redhat.com/show_bug.cgi?id=1196181

And skipped on s390x:
https://bugzilla.redhat.com/show_bug.cgi?id=1678277

python38.spec

@@ -978,6 +978,10 @@ CheckPython() {
   # our non-standard decorators take effect on the relevant tests:
   #   @unittest._skipInRpmBuild(reason)
   #   @unittest._expectedFailureInRpmBuild
+  # test_gdb skipped on armv7hl:
+  #   https://bugzilla.redhat.com/show_bug.cgi?id=1196181
+  # test_gdb skipped on s390x:
+  #   https://bugzilla.redhat.com/show_bug.cgi?id=1678277
   # test_asyncio skipped:
   #   https://bugs.python.org/issue35998
   WITHIN_PYTHON_RPM_BUILD= \
@@ -985,7 +989,9 @@ CheckPython() {
     -wW --slowest -j0 \
     -x test_distutils \
     -x test_bdist_rpm \
+    %ifarch %{arm} s390x
     -x test_gdb \
+    %endif
     %ifarch %{mips64}
     -x test_ctypes \
     %endif