Move declaration of keymap_config.

Should really not declare variables in .h files - since it's included
in different .c files, a proper linker then complains that the same
variable is declared more than once (once for each .c file that the
offending .h is included in).

tmk_core/common/keymap.c

@@ -24,6 +24,9 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "debug.h"
 #include "bootloader.h"
 
+#ifdef BOOTMAGIC_ENABLE
+extern keymap_config_t keymap_config;
+#endif
 
 static action_t keycode_to_action(uint8_t keycode);