[binutils-gdb] Factor out "Detaching from program" message printing

[sergiodj+buildbot at sergiodj dot net]

*** TEST RESULTS FOR COMMIT 0f48b757071509040d800ff9f7c8726e5828bd1a ***

Author: Pedro Alves <palves@redhat.com>
Branch: master
Commit: 0f48b757071509040d800ff9f7c8726e5828bd1a

Factor out "Detaching from program" message printing

Several targets have a copy of the same code that prints

 "Detaching from program ..."

in their target_detach implementation.  Factor that out to a common
function.

(For now, I left the couple targets that print this a bit differently
alone.  Maybe this could be further pulled out into infcmd.c.  If we
did that, and those targets want to continue printing differently,
this new function could be converted to a target method.)

gdb/ChangeLog:
2016-07-01  Pedro Alves  <palves@redhat.com>

	* darwin-nat.c (darwin_detach): Use target_announce_detach.
	* inf-ptrace.c (inf_ptrace_detach): Likewise.
	* nto-procfs.c (procfs_detach): Likewise.
	* remote.c (remote_detach_1): Likewise.
	* target.c (target_announce_detach): New function.
	* target.h (target_announce_detach): New declaration.