testsuite: Skip 90020.c on AIX.

Like HP/UX, AIX does not support undefined weak, so skip this test
in the testsuite.

	* gcc.dg/torture/pr90020.c: Skip on AIX..

gcc/testsuite/ChangeLog

 2020-04-23  David Edelsohn  <dje.gcc@gmail.com>
 
+	* gcc.dg/torture/pr90020.c: Skip on AIX.
+
+2020-04-23  David Edelsohn  <dje.gcc@gmail.com>
+
 	* g++.dg/cpp0x/lambda/pr94426-1.C: Require LTO.
 
 2020-04-23  Martin Sebor  <msebor@redhat.com>

gcc/testsuite/gcc.dg/torture/pr90020.c

 /* { dg-do run } */
-/* { dg-skip-if "No undefined weak" { hppa*-*-hpux* } } */
+/* { dg-skip-if "No undefined weak" { hppa*-*-hpux* || powerpc-ibm-aix* } } */
 /* { dg-require-weak "" } */
 /* { dg-additional-options "-Wl,-undefined,dynamic_lookup" { target *-*-darwin* } } */
 /* { dg-additional-options "-Wl,-flat_namespace" { target *-*-darwin[89]* } } */