VS2013: Adjust libgltf to 12.0 vcproj version

Change-Id: I076c998f5c843b60ac5624381e51271a0924043f
Reviewed-on: https://gerrit.libreoffice.org/10161Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>

external/libgltf/ExternalProject_libgltf.mk

@@ -43,6 +43,7 @@ $(call gb_ExternalProject_get_state_target,libgltf,build) :
 	$(call gb_ExternalProject_run,build,\
 		msbuild.exe libgltf.vcxproj \
 			/p:Configuration=$(if $(MSVC_USE_DEBUG_RUNTIME),Debug,Release) \
+			$(if $(filter 120,$(VCVER)),/p:PlatformToolset=v120 /p:VisualStudioVersion=12.0) \
 			$(if $(filter 110,$(VCVER)),/p:PlatformToolset=$(if $(filter 80,$(WINDOWS_SDK_VERSION)),v110,v110_xp) \
 				/p:VisualStudioVersion=11.0) \
 			$(if $(filter 100,$(VCVER)),/p:PlatformToolset=v100 \