Fix interrupt-noterm.exp on targets always in non-stop

Fix interrupt-noterm.exp on targets always in non-stop

With "maint set target-non-stop on" we get:

 @@ -66,13 +66,16 @@ Continuing.
  interrupt
  (gdb) PASS: gdb.base/interrupt-noterm.exp: interrupt

 -Program received signal SIGINT, Interrupt.
 -PASS: gdb.base/interrupt-noterm.exp: inferior received SIGINT
 -testcase src/gdb/testsuite/gdb.base/interrupt-noterm.exp completed in 0 seconds
 +[process 12119] #1 stopped.
 +0x0000003615ebc6d0 in __nanosleep_nocancel () at ../sysdeps/unix/syscall-template.S:81
 +81     T_PSEUDO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)
 +FAIL: gdb.base/interrupt-noterm.exp: inferior received SIGINT (timeout)
 +testcase src/gdb/testsuite/gdb.base/interrupt-noterm.exp completed in 10 seconds

That is, we get "[$thread] #1 stopped" instead of SIGINT.

The issue is that we don't currently distinguish send
"interrupt/ctrl-c" to target terminal vs "stop/pause" thread well;
both cases go through "target_stop".

And then, the native Linux backend (linux-nat.c) implements
target_stop with SIGSTOP in non-stop mode, and SIGINT in all-stop
mode.  Since "maint set target-non-stop on" forces the backend to be
always running in non-stop mode, even though the user-visible behavior
is "set non-stop" is "off", "interrupt" causes a SIGSTOP instead of
the SIGINT the test expects.

Fix this by introducing a target_interrupt method to use in the
"interrupt/ctrl-c" case, so "set non-stop off" can always work the
same irrespective of "maint set target-non-stop on/off".  I'm
explictly considering changing the "set non-stop on" behavior as out
of scope here.

Most of the patch is an across-the-board rename of to_stop hook
implementations to to_interrupt.  The only targets where something
more than a rename is being done are linux-nat.c and remote.c, which
are the only targets that support async, and thus are the only ones
the core side calls target_stop on.

gdb/ChangeLog:
2015-08-07  Pedro Alves  <palves@redhat.com>

	* darwin-nat.c (darwin_stop): Rename to ...
	(darwin_interrupt): ... this.
	(_initialize_darwin_inferior): Adjust.
	* gnu-nat.c (gnu_stop): Delete.
	(gnu_target): Don't install gnu_stop.
	* inf-ptrace.c (inf_ptrace_stop): Rename to ...
	(inf_ptrace_interrupt): ... this.
	(inf_ptrace_target): Adjust.
	* infcmd.c (interrupt_target_1): Use target_interrupt instead of
	target_stop.
	* linux-nat (linux_nat_stop): Rename to ...
	(linux_nat_interrupt): ... this.
	(linux_nat_stop): Reimplement.
	(linux_nat_add_target): Install linux_nat_interrupt.
	* nto-procfs.c (nto_interrupt_twice): Rename to ...
	(nto_handle_sigint_twice): ... this.
	(nto_interrupt): Rename to ...
	(nto_handle_sigint): ... this.  Call target_interrupt instead of
	target_stop.
	(procfs_wait): Adjust.
	(procfs_stop): Rename to ...
	(procfs_interrupt): ... this.
	(init_procfs_targets): Adjust.
	* procfs.c (procfs_stop): Rename to ...
	(procfs_interrupt): ... this.
	(procfs_target): Adjust.
	* remote-m32r-sdi.c (m32r_stop): Rename to ...
	(m32r_interrupt): ... this.
	(init_m32r_ops): Adjust.
	* remote-sim.c (gdbsim_stop_inferior): Rename to ...
	(gdbsim_interrupt_inferior): ... this.
	(gdbsim_stop): Rename to ...
	(gdbsim_interrupt): ... this.
	(gdbsim_cntrl_c): Adjust.
	(init_gdbsim_ops): Adjust.
	* remote.c (sync_remote_interrupt): Adjust comments.
	(remote_stop_as): Rename to ...
	(remote_interrupt_as): ... this.
	(remote_stop): Adjust comment.
	(remote_interrupt): New function.
	(init_remote_ops): Install remote_interrupt.
	* target.c (target_interrupt): New function.
	* target.h (struct target_ops) <to_interrupt>: New field.
	(target_interrupt): New declaration.
	* windows-nat.c (windows_stop): Rename to ...
	(windows_interrupt): ... this.
	* target-delegates.c: Regenerate.