Get Bison to build again when configured with --enable-gcc-warnings.

* src/location.c, src/location.h, src/main.c, src/scan-code.l: Add some
missing #include's.
* src/scan-code.l (handle_action_dollar, handle_action_at): Rename
loc argument as it shadows a global.
* src/scan-gram.l: Remove stray comma that prevents boundary_set
invocation.

* src/.cvsignore: Add scan-code.c.

src/location.c

@@ -21,8 +21,10 @@
 #include <config.h>
 #include "system.h"
 
+#include <mbswidth.h>
 #include <quotearg.h>
 
+#include "complain.h"
 #include "location.h"
 
 location const empty_location;