* lib/wait-process.h (wait_subprocess): Accept a new exitsignal argument.

* lib/wait-process.h (wait_subprocess): Accept a new exitsignal argument.
* lib/wait-process.c (wait_subprocess): Always set *exitsignal to 0 when
present and set it to the offending signal when the child exits due to
a signal.
* lib/csharpcomp.c, lib/execute.c, lib/javacomp.c: Update all callers.