Backport of upstream fix: https://git.netsurf-browser.org/netsurf.git/commit/?id=434f6c3fe7d1d2c6a3e6ae6338608a4a4421ab1b

https://bugs.netsurf-browser.org/mantis/view.php?id=2778
https://bugs.gentoo.org/835379
--- a/frontends/framebuffer/convert_font.c
+++ b/frontends/framebuffer/convert_font.c
@@ -290,14 +290,14 @@ bool generate_font_header(const char *path, struct font_data *data)
 
 
 	for (s = 0; s < 4; s++) {
-		fprintf(fp, "const uint8_t *%s_section_table;\n",
+		fprintf(fp, "extern const uint8_t *%s_section_table;\n",
 			var_lables[s]);
-		fprintf(fp, "const uint16_t *%s_sections;\n",
+		fprintf(fp, "extern const uint16_t *%s_sections;\n",
 			var_lables[s]);
 
 	}
 
-	fprintf(fp, "const uint8_t *font_glyph_data;\n");
+	fprintf(fp, "extern const uint8_t *font_glyph_data;\n");
 
 	fprintf(fp, "\n\n");