gdb: is_linked_with_cygwin_dll: mention filename in warning messages

gdb: is_linked_with_cygwin_dll: mention filename in warning messages

When a warning is displayed, it isn't clear to the user which file is
the cause of the warning.  Add the filename in there.  Remove the
"Failed to parse .idata section" part, since the .idata section is
always mentioned one way or another anyway, so it just contributes to
make the message longer than it needs to be.

gdb/ChangeLog:

	* windows-tdep.c (is_linked_with_cygwin_dll): Add filename to
	warning messages.