* exceptions.cc (signal_exit): Kill any executing child process if we're dying.

* path.h: Remove unneeded extern.
* spawn.cc (std_suffixes): Make static.  Don't set dwProcessId here since it
makes the process unsignalable.  Set strace flag that this is an execed process
stub.
* strace.cc (strace::vsprntf): Use strace flag to indicate when to visually
flag that this is an exec stub.
* include/sys/strace.h (strace): Add 'execing' flag.

winsup/cygwin/include/sys/strace.h

@@ -30,6 +30,7 @@ public:
   int version;
   int active;
   int lmicrosec;
+  int execing;
   strace() : version(1) {}
   void prntf (unsigned, const char *func, const char *, ...);
   void wm (int message, int word, int lon);