(ctrl_c_handler): Attempt to work around potential signal duplication during
process startup.
(sig_handle): Ignore SIGINT when we're just an "exec stub".
* spawn.cc (spawn_guts): Store pid of spawned process in global for use by
ctrl_c_handler.
* dcrt0.cc (dll_crt0_1): Call renamed initialization function.
* winsup.h: Reflect function name change.