enable pch for chartopengl

the pch file already exists, just needed to get compiled.

Change-Id: Ia9ff71b033a1508ed69696b8fd38ee8136393f42

chart2/Library_chartopengl.mk

@@ -17,6 +17,8 @@ $(eval $(call gb_Library_set_include,chartopengl,\
     $$(INCLUDE) \
 ))
 
+$(eval $(call gb_Library_set_precompiled_header,chartopengl,$(SRCDIR)/chart2/inc/pch/precompiled_chartopengl))
+
 $(eval $(call gb_Library_use_externals,chartopengl,\
 	boost_headers \
 	glm_headers \