More char constification

More char constification

Trivial constifications flagged by G++.  E.g.:

 src/gdb/c-varobj.c: In function ‘void c_describe_child(const varobj*, int, char**, value**, type**, char**)’:
 src/gdb/c-varobj.c:373:33: error: invalid conversion from ‘const char*’ to ‘char*’ [-fpermissive]
    char *join = was_ptr ? "->" : ".";
				  ^

gdb/ChangeLog:
2015-10-13  Pedro Alves  <palves@redhat.com>

	* ada-lang.c (ada_enum_name): Constify local.
	* ada-typeprint.c (print_range_bound): Constify locals.
	* c-varobj.c (c_describe_child): Likewise.
	* cli/cli-setshow.c (do_set_command): Likewise.
	* gdb_vecs.c (delim_string_to_char_ptr_vec_append): Likewise.
	* dwarf2read.c (find_file_and_directory): Likewise.
	(anonymous_struct_prefix, dwarf2_name): Likewise.
	* gnu-v3-abi.c (gnuv3_rtti_type): Likewise.
	* go-lang.c (unpack_mangled_go_symbol): Likewise.
	* jv-typeprint.c (java_type_print_base): Likewise.
	* ser-tcp.c (net_open): Likewise.
	* symfile.c (deduce_language_from_filename): Likewise.
	* symtab.c (gdb_mangle_name): Likewise.
	* tui/tui-io.c (tui_redisplay_readline): Likewise.