Check input interrupt first when reading packet

Hi,
I see timeout in one of several runs of random-signal.exp like this,

 $ (set -e; while true; do make check RUNTESTFLAGS="--target_board=native-gdbserver random-signal.exp"; done)

In about every five runs, we can see a fail,

PASS: gdb.base/random-signal.exp: continue
^CFAIL: gdb.base/random-signal.exp: stop with control-c (timeout)

after some investigation, I find '\003' may be discarded by GDBserver when
it is expecting '$'.  In GDB side, both normal packets and '\003' are sent
via function send, but GDBserver may receive them at any time, that is to
say, in the receive buffer in GDBserver, '\003' may appear before or after
normal packet.  However, current GDBserver doesn't handle this case.

With this patch applied, I don't see this fail in multiple runs.
Although there is still timeout fail, that is a different problem, the
next patch will fix it.

gdb/gdbserver:

2016-01-08  Yao Qi  <yao.qi@linaro.org>

	* remote-utils.c (getpkt): If c is '\003', call target hook
	request_interrupt.

2 files changed, 14 insertions, 0 deletions

diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index 0c9e73e..1c73f8b 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,8 @@
+2016-01-08  Yao Qi  <yao.qi@linaro.org>
+
+	* remote-utils.c (getpkt): If c is '\003', call target hook
+	request_interrupt.
+
 2016-01-06  Yao Qi  <yao.qi@linaro.org>
 
 	* linux-aarch32-low.h (arm_abi_breakpoint): Move to
diff --git a/gdb/gdbserver/remote-utils.c b/gdb/gdbserver/remote-utils.c
index 5f43820..c5f4647 100644
--- a/gdb/gdbserver/remote-utils.c
+++ b/gdb/gdbserver/remote-utils.c
@@ -959,6 +959,15 @@ getpkt (char *buf)
       while (1)
 	{
 	  c = readchar ();
+
+	  /* The '\003' may appear before or after each packet, so
+	     check for an input interrupt.  */
+	  if (c == '\003')
+	    {
+	      (*the_target->request_interrupt) ();
+	      continue;
+	    }
+
 	  if (c == '$')
 	    break;
 	  if (remote_debug)