* gdb/objc-lang.c (objc_printstr): Add width arg to match

* gdb/objc-lang.c (objc_printstr): Add width arg to match
printstr prototype.
(compare_selectors): Add 'const' to arg types.
(compare_classes): Likewise.
(find_imps): Cast msym pointer to avoid compiler warning.
(print_object_command): Validate the address before
passing it to the print routine.
(find_objc_msgcall_submethod): Change function argument to
return an int.
* objc-lang.h: Add 'extern' to all function declaration.
(value_nsstring): Add declaration.