move platform toolset retrieval to VcprojGenerator

In a subsequent commit we will need access to more information of the
project object. This is merely a refactoring.

Change-Id: I40e501d037eb7d0295e1057e7b86e404e88e6ca3
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Windows XP target support for MSVC >= 2012

To enable windows xp support, we must do two things:
1. linker flag must be /SUBSYSTEM:CONSOLE,5.01 or
   /SUBSYSTEM:WINDOWS,5.01. For x64, the version is 5.02.
2. Do not use Windows Kit 8. Win SDK v7.1A is recommended. Prepend the
   right include paths and lib paths to INCLUDE and LIB before
   building.

The Windows XP target support is enabled by passing "-target xp" to
configure.

Task-number: QTBUG-29939

Change-Id: I84c8439606cc2a9d27d64947702846faa4f1e4a2
Reviewed-by: Lucas Wang <wbsecg1@gmail.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
vcxproj generator: append version suffix only to library targets

Task-number: QTBUG-38066
Change-Id: I2f1635f2cb34acb388c380fc2fc3fbe4df04bb03
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
do not define QT_NO_STYLE_S60 on Windows

This isn't needed anymore since quite a while.

Change-Id: I80a99f988a917af5b8c64865ec7e73e519978740
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>