Fix objcopy's --preserve-dates command line option so that it will work with PE format files.

	PR binutils/pr25662
bfd	* libcoff-in.h (struct pe_tdata): Rename the insert_timestamp
	field to timestamp and make it an integer.
	* libcoff.h: Regenerate.
	* peXXigen.c (_bfd_XXi_only_swap_filehdr_out): Test the timestamp
	field in the pe_data structure rather than the insert_timestamp
	field.

binutils* objcopy.c (copy_object): When copying PE format files set the
	timestamp field in the pe_data structure if the preserve_dates
	flag is set.
	* testsuite/binutils-all/objcopy.exp (objcopy_test) Use
	--preserve-dates in place of the -p option, in order to make its
	effect more obvious.

ld	* emultempl/pe.em (after_open): Replace initialisation of the
	insert_timestamp field in the pe_data structure with an
	initialisation of the timestamp field.
	* emultemp/pep.em: Likewise.
	* pe-dll.c (fill_edata): Use the timestamp field in the pe_data
	structure instead of the insert_timestamp field.