fix doc generation for MSVC toolchain

Change-Id: If6214f431f37bd98b4029dade32bb62fcd746292
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>
setup-qt: check whether Qt is debug, release or both

Introduce Qt.core.debugReleaseBuild for that.

Change-Id: Ib448f4606cc1896378a511251815faa3b7563e86
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@digia.com>
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>