Use GTEST_SKIP() instead of early return.

The issue for iOS platforms was fixed by crrev.com/c/2505276.

Bug: webrtc:13057
Change-Id: I0f01c1291184f4c7960db746951255961a962303
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/228520
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Alessio Bazzica <alessiob@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34740}

system_wrappers/source/denormal_disabler_unittest.cc

@@ -132,8 +132,8 @@ TEST(DenormalDisabler, ZeroDenormalsNested) {
 // compiler are not supported.
 TEST(DenormalDisabler, DoNotZeroDenormalsIfUnsupported) {
   if (DenormalDisabler::IsSupported()) {
-    // TODO(bugs.webrtc.org/13057): Use GTEST_SKIP() once fixed.
-    return;
+    GTEST_SKIP() << "This test should only run on platforms without support "
+                    "for DenormalDisabler.";
   }
   DenormalDisabler denormal_disabler(/*enabled=*/true);
   for (float x : kDenormalDivisors) {