Make signal handling work well across platforms

- Fix sigsuspend() on XNU
- Fix strsignal() on non-Linux
- Add unit tests for strsignal()
- Add unit tests for setitimer()
- Add unit tests for sigsuspend()
- Rewrite setitimer() for New Technology
- Rewrite nanosleep() for New Technology
- Polyfill SIGALRM on the New Technology
- select(0,0,0,0) on NT now calls pause()
- Remove some NTDLL calls that aren't needed
- Polyfill SA_NOCLDWAIT on the New Technology
- Polyfill SA_RESETHAND on the New Technology
- Polyfill sigprocmask() on the New Technology
- Polyfill SIGCHLD+SIG_IGN on the New Technology
- Polyfill SA_RESTART masking on the New Technology
- Deliver console signals from main thread on New Technology
- Document SA_RESTART behavior w/ @sarestartable / @norestart
- System call trace in MODE=dbg now prints inherited FDs and signal mask

libc/calls/write-nt.c

@@ -27,6 +27,7 @@
 #include "libc/nt/files.h"
 #include "libc/nt/runtime.h"
 #include "libc/nt/struct/overlapped.h"
+#include "libc/runtime/internal.h"
 #include "libc/str/str.h"
 #include "libc/sysv/consts/sig.h"
 #include "libc/sysv/errfuns.h"
@@ -35,6 +36,7 @@ static textwindows ssize_t sys_write_nt_epipe(int fd) {
   siginfo_t info;
   STRACE("WriteFile(%d:%p) → %m", fd, g_fds.p[fd].handle);
   if (!__sighandrvas[SIGPIPE]) {
+    __restorewintty();
     _Exit(128 + SIGPIPE);
   } else if (__sighandrvas[SIGPIPE] >= kSigactionMinRva) {
     bzero(&info, sizeof(info));