Fix control-c handling on Windows

As Hannes pointed out, the Windows target-async patches broke C-c
handling there.  Looking into this, I found a few oddities, fixed
here.

First, windows_nat_target::interrupt calls GenerateConsoleCtrlEvent.
I think this event can be ignored by the inferior, so it's not a great
way to interrupt.  Instead, using DebugBreakProcess (or a more
complicated thing for Wow64) seems better.

Second, windows_nat_target did not implement the pass_ctrlc method.
Implementing this lets us remove the special code to call
SetConsoleCtrlHandler and instead integrate into gdb's approach to C-c
handling.  I believe that this should also fix the race that's
described in the comment that's being removed.

Initially, I thought a simpler version of this patch would work.
However, I think what happens is that some other library (I'm not sure
what) calls SetConsoleCtrlHandler while gdb is running, and this
intercepts and handles C-c -- so that the gdb SIGINT handler is not
called.  C-break continues to work, presumably because whatever
handler is installed ignores it.

This patch works around this issue by ensuring that the gdb handler
always comes first.

1 files changed, 10 insertions, 0 deletions

diff --git a/gdb/inferior.h b/gdb/inferior.h
index 547e875..6fc0a30 100644
--- a/gdb/inferior.h
+++ b/gdb/inferior.h
@@ -178,6 +178,16 @@ extern tribool is_gdb_terminal (const char *tty);
 
 extern tribool sharing_input_terminal (int pid);
 
+/* The type of the function that is called when SIGINT is handled.  */
+
+typedef void c_c_handler_ftype (int);
+
+/* Install a new SIGINT handler in a host-dependent way.  The previous
+   handler is returned.  It is fine to pass SIG_IGN for FN, but not
+   SIG_DFL.  */
+
+extern c_c_handler_ftype *install_sigint_handler (c_c_handler_ftype *fn);
+
 extern void child_terminal_info (struct target_ops *self, const char *, int);
 
 extern void child_terminal_ours (struct target_ops *self);