qmake: do not exclusively lock files for reading on Windows/MSVC

qmake: do not exclusively lock files for reading on Windows/MSVC

When sifting through a file to find Q_OBJECT and friends, qmake
was locking it for reading and writing (_SH_DENYRW).
This breaks parallel builds where multiple qmake instances might want
to scan the same file.
Changed the sharing constant to _SH_DENYNO, which doesn't lock the
file at all. This is consistent with the _sopen_s call in findDeps.

Change-Id: I9c0a06db7f580f411e79d9d96dd36a6d705679aa
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>