comdat_hash memory leaks

Entries added to the hash table with bfd_malloc ought to be freed when
the hash table is deleted.  This patch adds the necessary del_f to the
htab_create call, and delays creating the table until an
IMAGE_SCN_LNK_COMDAT symbol is read.

	* peicode.h (pe_mkobject): Move comdat_hash creation..
	(htab_hash_flags, htab_eq_flags): ..and these support functions..
	* coffcode.h (handle_COMDAT): ..to here, renaming support to
	(comdat_hashf, comdat_eqf): ..this and adding..
	(comdat_delf): ..this new function.