Visual Studio automatically defines _WINDLL when building a DLL,
regardless of project settings
(https://msdn.microsoft.com/en-us/library/8x480de8.aspx). This define
is therefore widely used to detect DLL vs. static library or executable
build target on Windows.
For makefiles, _WINDLL need to be manually defined, which QMake failed
to do so far.
Task-number: QTBUG-55183
Change-Id: Ic62201666c44e730e6881706d568ce9eaf22b7a4
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
b6f5b38f8c