gbuild: gb_LinkTarget__get_headers_check can signal error now
gbuild: gb_LinkTarget__get_headers_check can signal error now

... since no external link targets not with gbuild should be used via
gb_LinkTarget_use_library/static_library.

Change-Id: I1c3188dbbe2eaa2f5acfb8944a79ad3b67a95998

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core