Add cygwin_internal() operation to retrieve the EXCEPTION_RECORD from a siginfo_t *

* external.cc (cygwin_internal): Add operation to retrieve a copy
	of the EXCEPTION_RECORD from a siginfo_t *.
	* include/sys/cygwin.h (cygwin_getinfo_types): Ditto.
	* exception.h (cygwin_exception): Add exception_record accessor.

Signed-off-by: Jon TURNEY <jon.turney@dronecode.org.uk>

winsup/cygwin/exception.h

@@ -175,4 +175,5 @@ public:
     framep (in_framep), ctx (in_ctx), e (in_e), h (NULL) {}
   void dumpstack ();
   PCONTEXT context () const {return ctx;}
+  EXCEPTION_RECORD *exception_record () const {return e;}
 };