Use consistent collation testability criteria in corelib/text

tst_qstringapisymmetry needs to use the same collation testability
criteria as tst_qcollator, that is, the locales that may be tested
without ICU and not on Mac nor Windows are only the system locale and
C locale.

Task-number: QTBUG-109954
Change-Id: I69f19ae28b3a16b3827c1eee62ae59fcfdf45209
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

tests/auto/corelib/text/qstringapisymmetry/tst_qstringapisymmetry.cpp

@@ -1482,8 +1482,9 @@ void tst_QStringApiSymmetry::localeAwareCompare_data()
         return false;
     };
 #else
-    // Otherwise, trust that setlocale() reconfigures QString::localeAwareCompare():
-    const auto canTest = [](const char *) { return true; };
+    const auto canTest = [](const char *wanted) {
+        return QLocale(wanted) == QLocale::c() || QLocale(wanted) == QLocale::system().collation();
+    };
 #endif
     // Update tailpiece's max-value for this if you add a new locale group
     int countGroups = 0;