Enable building with clang / libc++ on OS X 10.9 Mavericks

A minimalistic change to enable building with clang / libc++ on OS X
10.9 Mavericks. The configure script now avoids overriding build
settings when using clang/libc++. Added a new build configuration with
settings specific to clang/libc++ on OS X.

Task-number: QTBUG-34652

Change-Id: Iaedaff7c06e9818a5f2ee0d6db93fbe3b2e65e28
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>
Use qt_mac_effectiveview_for for setFocus_sys

Currently setFocus_sys use qt_mac_nativeview_for to set the focus which
triggers a bug rerouting the key events through NSMenu rather that
directly to the correct widget. Get the effective id returns the
correct widget. This changeset applies the patch proposed in the bug
report

Task-number: QTBUG-34371
Change-Id: I0831f41ca409ff309954bb45a50975dd4eb1406a
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>
Completely bootstrap idc.

idc dynamically loads libraries depending on QtCore.dll
whose static instances can then cause clashes.

Task-number: QTBUG-35275

Change-Id: I48bb9c4b4ab33b1909d650458c0351c008b46ac0
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
(cherry picked from qtactiveqt/ab3e8e80fbd81a38039c713189b0422972e0963e)
Don't use Standard Library routines in qthread_p.h

Just write the for loops by hand so we don't need to use the Standard
Library. That's necessary to support a -no-stl build.

This patch is not necessary in Qt 5 since Qt 5 does not have -no-stl.

Task-number: QTBUG-35424
Change-Id: Id449d807eaf7350f1a668ef16d356a9e236c6058
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>