fix build with glm 0.9.9

In file included from /usr/include/glm/gtx/norm.hpp:18:0,
                 from /data/rene/git/LibreOffice/master/vcl/inc/opengl/VertexUti
ls.hxx:16,
                 from /data/rene/git/LibreOffice/master/vcl/inc/opengl/LineRende
rUtils.hxx:14,
                 from /data/rene/git/LibreOffice/master/vcl/opengl/LineRenderUti
ls.cxx:11:
/usr/include/glm/gtx/quaternion.hpp:23:3: error: #error "GLM: GLM_GTX_quaternion
 is an experimental extension and may change in the future. Use #define GLM_ENABLE_EXPERIMENTAL before including it, if you really want to use it."
 # error "GLM: GLM_GTX_quaternion is an experimental extension and may change in the future. Use #define GLM_ENABLE_EXPERIMENTAL before including it, if you really want to use it."
   ^~~~~

so just define it.

Change-Id: I981bfb5fd944f32a3774b3f9b183989773bf235f

chart2/Library_chartcore.mk

@@ -23,6 +23,12 @@ $(eval $(call gb_Library_add_defs,chartcore,\
     -DOOO_DLLIMPLEMENTATION_CHARTVIEW \
 ))
 
+ifeq ($(SYSTEM_GLM),TRUE)
+$(eval $(call gb_Library_add_defs,chartcore,\
+        -DGLM_ENABLE_EXPERIMENTAL \
+))
+endif
+
 $(eval $(call gb_Library_set_precompiled_header,chartcore,$(SRCDIR)/chart2/inc/pch/precompiled_chartcore))
 
 $(eval $(call gb_Library_use_externals,chartcore,\

vcl/Library_vcl.mk

@@ -49,6 +49,12 @@ $(eval $(call gb_Library_add_defs,vcl,\
 	-DENABLE_MERGELIBS=$(if $(MERGELIBS),1,0) \
 ))
 
+ifeq ($(SYSTEM_GLM),TRUE)
+$(eval $(call gb_Library_add_defs,vcl,\
+        -DGLM_ENABLE_EXPERIMENTAL \
+))
+endif
+
 $(eval $(call gb_Library_use_sdk_api,vcl))
 
 $(eval $(call gb_Library_use_custom_headers,vcl,\