combine: Use TDF_DETAILS for "can't combine" dump prints

combine: Use TDF_DETAILS for "can't combine" dump prints

Some people use the -fdump-rtl-combine dumps (instead of the -da or
-fdump-rtl-combine-all dump), but the "Can't combine iN into iM"
messages do not make any sense if the failed combine attempts are not
printed otherwise.  So let's change that.

	* combine.c (try_combine): Do not print "Can't combine" messages unless
	printing failed combination attempts.

From-SVN: r268453