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`

third_party/compiler_rt/udivti3.c

@@ -1,14 +0,0 @@
-#if 0
-/*─────────────────────────────────────────────────────────────────╗
-│ To the extent possible under law, Justine Tunney has waived      │
-│ all copyright and related or neighboring rights to division,     │
-│ as it is written in the following disclaimers:                   │
-│   • http://unlicense.org/                                        │
-│   • http://creativecommons.org/publicdomain/zero/1.0/            │
-╚─────────────────────────────────────────────────────────────────*/
-#endif
-#include "third_party/compiler_rt/int_lib.h"
-
-COMPILER_RT_ABI tu_int __udivti3(tu_int a, tu_int b) {
-  return __udivmodti4(a, b, NULL);
-}