mkqt5bld: Fix make install on Windows for QNX

Most of the 'black magic' for Android on Windows applies to
QNX on Windows.

also mark QNX as a non-desktop build.

Change-Id: Ia1582088c3ebc4bfa3fb158dd760c38c70592bb7
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>