Make improvements

- Fix unused local variable errors
- Remove yoinks from sigaction() header
- Add nox87 and aarch64 to github actions
- Fix cosmocc -fportcosmo in linking mode
- It's now possible to build `make m=llvm o/llvm/libc`

libc/calls/sigignore.c

@@ -27,5 +27,5 @@ int sigignore(int sig) {
   struct sigaction sa;
   bzero(&sa, sizeof(sa));
   sa.sa_handler = SIG_IGN;
-  return (sigaction)(sig, &sa, 0);
+  return sigaction(sig, &sa, 0);
 }