(conan-io#14734) qt6: allow gcc11 and clang12 consumers

* qt6: allow gcc11 and clang12 consumers

* fixup

* re-fixup

recipes/qt/6.x.x/conanfile.py

@@ -249,9 +249,11 @@ def _enablemodule(mod):
                 _enablemodule(module)
 
     def validate(self):
-        if self.info.settings.compiler == "gcc" and Version(self.info.settings.compiler.version) >= "11" or \
-            self.info.settings.compiler == "clang" and Version(self.info.settings.compiler.version) >= "12":
-            raise ConanInvalidConfiguration("qt is not supported on gcc11 and clang >= 12 on C3I until conan-io/conan-center-index#13472 is fixed")
+        if os.getenv('NOT_ON_C3I', '0') == '0':
+            if self.info.settings.compiler == "gcc" and Version(self.info.settings.compiler.version) >= "11" or \
+                self.info.settings.compiler == "clang" and Version(self.info.settings.compiler.version) >= "12":
+                raise ConanInvalidConfiguration("qt is not supported on gcc11 and clang >= 12 on C3I until conan-io/conan-center-index#13472 is fixed\n"\
+                                                "If your distro is modern enough (xcb >= 1.12), set environment variable NOT_ON_C3I=1")
 
         # C++ minimum standard required
         if self.settings.compiler.get_safe("cppstd"):