This enables the mainConfig optimization in all threads,
and ensures the user warning only happens in the main thread.

The test-mode-enabled logic is only really useful in the main thread,
but it's simpler to just do it in all threads.

REVIEW: 118985

Visual C++ 2010 throws an internal compiler error trying to compile
kconfigtest, since 5f4dc2973f. I couldn't figure out a non-intrusive
code tweak that would work around the ICE, so I had to skip compiling
this particular initialization code on this particular compiler version,
and skip running the test that relies on it (testEnums).

The dummy=42 entry is so that the config group isn't empty,
which makes testGroupCopyTo and testReparent still run and pass,
so we don't need to skip them.

REVIEW:118852

- QLocale::QLocale::Austria
+ QLocale::Austria

I'm surprised this worked in gcc in the CI...