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/samplepids.c

@@ -16,7 +16,9 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/assert.h"
 #include "libc/calls/internal.h"
+#include "libc/dce.h"
 #include "libc/rand/lcg.internal.h"
 
 /**
@@ -28,13 +30,15 @@
  *
  * @return number of items returned in pids and handles
  */
-int __sample_pids(int pids[hasatleast 64], int64_t handles[hasatleast 64]) {
+textwindows int __sample_pids(int pids[hasatleast 64],
+                              int64_t handles[hasatleast 64],
+                              bool exploratory) {
   static uint64_t rando = 1;
   uint32_t i, j, base, count;
   base = KnuthLinearCongruentialGenerator(&rando);
   for (count = i = 0; i < g_fds.n; ++i) {
     j = (base + i) % g_fds.n;
-    if (g_fds.p[j].kind == kFdProcess) {
+    if (g_fds.p[j].kind == kFdProcess && (!exploratory || !g_fds.p[j].zombie)) {
       pids[count] = j;
       handles[count] = g_fds.p[j].handle;
       if (++count == 64) {