Constify arguments of gdb_bfd_lookup_symbol and related functions

Constify arguments of gdb_bfd_lookup_symbol and related functions

Fixes this error:

/home/pedro/gdb/mygit/src/gdb/solib-frv.c: In function ‘int enable_break2()’:
/home/pedro/gdb/mygit/src/gdb/solib-frv.c:622:72: error: invalid conversion from ‘const void*’ to ‘void*’ [-fpermissive]
       addr = gdb_bfd_lookup_symbol (tmp_bfd, cmp_name, "_dl_debug_addr");
                                                                        ^
In file included from /home/pedro/gdb/mygit/src/gdb/solib-frv.c:23:0:
/home/pedro/gdb/mygit/src/gdb/solib.h:82:18: error:   initializing argument 3 of ‘CORE_ADDR gdb_bfd_lookup_symbol(bfd*, int (*)(asymbol*, void*), void*)’ [-fpermissive]
 extern CORE_ADDR gdb_bfd_lookup_symbol (bfd *abfd,
                  ^

The call in question is:

      addr = gdb_bfd_lookup_symbol (tmp_bfd, cmp_name, "_dl_debug_addr");

gdb/ChangeLog:

	* solib-dsbt.c (cmp_name): Constify arguments.
	* solib-frv.c (cmp_name): Likewise.
	* solib-svr4.c (svr4_create_solib_event_breakpoints): Likewise.
	* solib.c (gdb_bfd_lookup_symbol_from_symtab): Likewise.
	(bfd_lookup_symbol_from_dyn_symtab): Likewise.
	(gdb_bfd_lookup_symbol): Likewise.
	* solib.h (gdb_bfd_lookup_symbol): Likewise.
	(gdb_bfd_lookup_symbol_from_symtab): Likewise.