Reenable test_gdb on x86_64

The test was disabled for Python 3.6.4 where it fails currently, but it
completes successfully on Python 3.7. See commit:
d84538b320

Enable also runnig test_gdb on aarch64, as failures are no longer observed.
The bugzilla associated with the reqson why it was disabled is long closed.
See commit: 3b7dcebf39

python37.spec

@@ -1065,10 +1065,12 @@ CheckPython() {
     -wW --slowest --findleaks \
     -x test_distutils \
     -x test_bdist_rpm \
-    -x test_gdb \
     %ifarch %{mips64}
     -x test_ctypes \
     %endif
+    %ifarch %{power64} s390 s390x armv7hl %{mips}
+    -x test_gdb \
+    %endif
     %ifarch ppc64le
     -x test_buffer \
     %endif