Detect _exit by matching the _exit breakpoint

This should work more consistently than looking for a call to
__internal_syscall, which was very library specific.

testsuite/ChangeLog:

	* config/ri5cyverilator.exp (beebs_load): Check for
	_exit breakpoint instead of __internal_syscall when trying
	to detect exit.

testsuite/ChangeLog

@@ -1,3 +1,9 @@
+2019-04-23  Edward Jones  <[email protected]>
+
+	* config/ri5cyverilator.exp (beebs_load): Check for
+	_exit breakpoint instead of __internal_syscall when trying
+	to detect exit.
+
 2019-04-10  Jeremy Bennett  <[email protected]>
 
 	This gives greater flexibility when testing with BEEBS.  The

testsuite/config/ri5cyverilator.exp

@@ -95,7 +95,7 @@ proc beebs_load { file } {
     # _exit and check its argument instead).
     send "cont\n"
     expect {
-      -re ".*__internal_syscall.*n=93.*" {
+      -re ".*stopped.*_exit.*" {
         send "print \$a0\n"
       }
       timeout {