Port a lot more code to AARCH64

- Introduce epoll_pwait()
- Rewrite -ftrapv and ffs() libraries in C code
- Use more FreeBSD code in math function library
- Get significantly more tests passing on qemu-aarch64
- Fix many Musl long double functions that were broken on AARCH64

test/libc/stdio/fwrite_test.c

@@ -173,7 +173,7 @@ TEST(fwrite, signalStorm) {
   if (!pid) {
     do {
       ASSERT_NE(-1, kill(getppid(), SIGINT));
-      usleep(1);
+      usleep(25);
     } while (!gotsigint);
     _exit(0);
   }