Implement pause.

Author: sunfishcode

expected/wasm32-wasi/defined-symbols.txt

@@ -785,6 +785,7 @@ optind
 optopt
 optreset
 pathconf
+pause
 perror
 poll
 posix_fadvise

libc-bottom-half/sources/pause.c

@@ -0,0 +1,7 @@
+#include <unistd.h>
+#include <wasi.h>
+
+int pause(void) {
+    size_t n;
+    (void)__wasi_poll_oneoff(0, 0, 0, &n);
+}