Make fixes and improvements

- Document more compiler flags
- Expose new __print_maps() api
- Better overflow checking in mmap()
- Improve the shell example somewhat
- Fix minor runtime bugs regarding stacks
- Make kill() on fork()+execve()'d children work
- Support CLONE_CHILD_CLEARTID for proper joining
- Fix recent possible deadlock regression with --ftrace

libc/calls/wincrash.c

@@ -35,6 +35,7 @@ privileged unsigned __wincrash(struct NtExceptionPointers *ep) {
   int sig, code;
   ucontext_t ctx;
   STRACE("__wincrash");
+
   switch (ep->ExceptionRecord->ExceptionCode) {
     case kNtSignalBreakpoint:
       code = TRAP_BRKPT;