I caught a few mingw32-specific failures for some of the gdb.reverse

I caught a few mingw32-specific failures for some of the gdb.reverse
tests.

FAIL: gdb.reverse/consecutive-precsave.exp: reload precord save file
FAIL: gdb.reverse/finish-precsave.exp: reload precord save file
FAIL: gdb.reverse/until-precsave.exp: reload core file
FAIL: gdb.reverse/watch-precsave.exp: reload core file
FAIL: gdb.reverse/step-precsave.exp: reload core file
FAIL: gdb.reverse/break-precsave.exp: reload precord save file
FAIL: gdb.reverse/sigall-precsave.exp: reload precord save file

They happen for two reasons.

- mingw32 does not define SIGTRAP, so upon recording a core file, the
signal information will be missing, which in turn causes GDB to not
display the stopping signal when it loads the same core file.  An
earlier message warns about this:

"warning: Signal SIGTRAP does not exist on this system."

- The testcase is crafted in a way that expects a pattern of the
stopping signal message instead of a successful core file read message.

The following patch fixes this by changing the old pattern to a more
reasonable one, while still ignoring the fact that mingw32-based GDB
does not record a SIGTRAP in a core file because it does not define
it.

gdb/testsuite/

2014-11-18  Luis Machado  <lgustavo@codesourcery.com>

	* gdb.reverse/break-precsave: Expect completion message for
	core file reads.
	* gdb.reverse/consecutive-precsave.exp: Likewise.
	* gdb.reverse/finish-precsave.exp: Likewise.
	* gdb.reverse/i386-precsave.exp: Likewise.
	* gdb.reverse/machinestate-precsave.exp: Likewise.
	* gdb.reverse/sigall-precsave.exp: Likewise.
	* gdb.reverse/solib-precsave.exp: Likewise.
	* gdb.reverse/step-precsave.exp: Likewise.
	* gdb.reverse/until-precsave.exp: Likewise.
	* gdb.reverse/watch-precsave.exp: Likewise.