Set breakpoint on the right line

In gdb.base/watchpoint-hw-hit-once.exp, test scans source and set
breakpoint on the line having "break-at-exit",

  gdb_breakpoint [gdb_get_line_number "break-at-exit"]

However, in watchpoint-hw-hit-once.c, there are two lines having
this key word:

  dummy = 1;	/* Stub to catch break-at-exit after WATCHEE has been hit.  */
  dummy = 2;	/* break-at-exit */

so the test sets breakpoint on the first one, while I think it is
expected to set breakpoint on the second one, as far as I can tell
from the comments in watchpoint-hw-hit-once.c:

  /* Stub lines are present as no breakpoints/watchpoint gets hit if current PC
     already stays on the line PC while entering "step"/"continue".  */

This patch is to change the source matching pattern so that test
can correctly set breakpoint on the right line.  This patch fixes
a fail we found on arm-none-eabi target.

(gdb) PASS: gdb.base/watchpoint-hw-hit-once.exp: continue
continue^M
Continuing.^M
^M
*** EXIT code 0^M
[Inferior 1 (Remote target) exited normally]^M
(gdb) FAIL: gdb.base/watchpoint-hw-hit-once.exp: continue to break-at-exit (the program exited)

Run it again on x86_64-linux, no result changes.

gdb/testsuite:

2014-08-19  Yao Qi  <yao@codesourcery.com>

	* gdb.base/watchpoint-hw-hit-once.exp: Set breakpoint on the
	right line.

gdb/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2014-08-19  Yao Qi  <yao@codesourcery.com>
+
+	* gdb.base/watchpoint-hw-hit-once.exp: Set breakpoint on the
+	right line.
+
 2014-08-18  David Blaikie  <dblaikie@gmail.com>
 
 	* boards/fission.exp: Explicitly pass -ggnu-pubnames for clang.

gdb/testsuite/gdb.base/watchpoint-hw-hit-once.exp

@@ -29,7 +29,7 @@ if ![runto_main] {
 
 gdb_test "rwatch watchee"
 
-gdb_breakpoint [gdb_get_line_number "break-at-exit"]
+gdb_breakpoint [gdb_get_line_number "dummy = 2"]
 
 gdb_test "continue" "Continuing.\r\nHardware read watchpoint \[0-9\]+: watchee\r\n\r\nValue = 0\r\n.*"