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/sock/kntwsadata.c

@@ -38,6 +38,7 @@ _Hide struct NtWsaData kNtWsaData;
 
 static textwindows void WinSockCleanup(void) {
   int i, rc;
+  (void)rc;
   rc = WSACleanup();
   NTTRACE("WSACleanup() → %d% lm", rc);
 }