qmake/MSVC: fix parsing of the /openmp option

Task-number: QTBUG-29143

Change-Id: I6b1ce0babf51701fa404b821b22060a87c4f46b2
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
(cherry picked from commit be8c47b1404257e33d6b7866101167726a3d1c30)
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
qmake/MSVC: do not disable buffer security check per default

The default must be "unset" to let the user's MSVC settings decide
what the default value is.

Task-number: QTBUG-29329

Change-Id: I6015202c123dbb7304941b0d24557a26a1e3236c
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
(cherry picked from commit 4fe029963d375675d3d4ddaea7e1767486228a73)
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
do not parse MSVC option /Gs as /GS

/Gs[size] will be added as additional option as there is no XML element
for this option.

Task-number: QTBUG-29329

Change-Id: I1f09bfdac90f9c5f2333dc03e6e4e6a206b4f6d0
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
(cherry picked from commit 9c1628aae3d3a7a5f935caa10f838ca24832c5f5)