Add WIN32 flag to SWIG csharp command line

[szekerest]

As of the cmake build, the WIN32 flag for the SWIG command line hasn't been added, though it was present in the nmake based builds.
This results in the GEOS exceptions to cause app crashes like this:

	Exception #:  0XE06D7363
	Stack:        
		KERNELBASE!RaiseException+0x68
		VCRUNTIME140!CxxThrowException+0xad
		geos!geos::operation::buffer::BufferBuilder::bufferLineSingleSided+0xe9a
		geos_c!GEOSOffsetCurve_r+0x10e
		mapserver!msGEOSOffsetCurve+0x70 [e:\builds-t1\src\mapserver-intramaps\mapgeos.c @ 807]
		mapserver!msOffsetCurve+0x24 [e:\builds-t1\src\mapserver-intramaps\maputil.c @ 1764]
		mapserver!msDrawLineSymbol+0x18d [e:\builds-t1\src\mapserver-intramaps\maprendering.c @ 601]
		mapserver!msDrawShadeSymbol+0xc5 [e:\builds-t1\src\mapserver-intramaps\maprendering.c @ 705]
		mapserver!polygonLayerDrawShape+0xdd [e:\builds-t1\src\mapserver-intramaps\mapdraw.c @ 1928]
		mapserver!msDrawShape+0x7b5 [e:\builds-t1\src\mapserver-intramaps\mapdraw.c @ 2173]
		mapserver!msDrawVectorLayer+0x804 [e:\builds-t1\src\mapserver-intramaps\mapdraw.c @ 1175]
		mapserver!msDrawLayer+0x3a3 [e:\builds-t1\src\mapserver-intramaps\mapdraw.c @ 813]
		mapserver!msDrawMap+0x415 [e:\builds-t1\src\mapserver-intramaps\mapdraw.c @ 403]
		mapscript!CSharp_mapObj_draw+0xd

and this

Exception #:  0XE06D7363
	Stack:        
		KERNELBASE!RaiseException+0x68
		VCRUNTIME140!CxxThrowException+0xad
		geos!geos::operation::buffer::BufferBuilder::bufferLineSingleSided+0xe9a
		geos_c!GEOSOffsetCurve_r+0x10e
		mapserver!msGEOSOffsetCurve+0x70 [e:\builds-t1\src\mapserver-intramaps\mapgeos.c @ 807]
		mapserver!msOffsetCurve+0x24 [e:\builds-t1\src\mapserver-intramaps\maputil.c @ 1764]
		mapserver!msDrawLineSymbol+0x18d [e:\builds-t1\src\mapserver-intramaps\maprendering.c @ 601]
		mapserver!msDrawShadeSymbol+0xc5 [e:\builds-t1\src\mapserver-intramaps\maprendering.c @ 705]
		mapserver!msDrawLegendIcon+0xb18 [e:\builds-t1\src\mapserver-intramaps\maplegend.c @ 328]
		mapscript!CSharp_classObj_drawLegendIcon+0xe3