Without the change builds fails on upstream gcc-10 as:
ld: label.o:src/template-history.h:31: multiple definition of `gl_template_history'; glabels-batch.o:src/template-history.h:31: first defined here
ld: label-text.o:src/font-history.h:31: multiple definition of `gl_font_history'; glabels-batch.o:src/font-history.h:31: first defined here
ld: font-history.o:src/font-history.h:31: multiple definition of `gl_font_history'; glabels-batch.o:src/font-history.h:31: first defined here
ld: template-history.o:src/template-history.h:31: multiple definition of `gl_template_history'; glabels-batch.o:src/template-history.h:31: first defined here