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/python/Modules/cjkcodecs/__cp950ext_decmap.c

@@ -1,4 +1,5 @@
 #include "libc/x/x.h"
+#include "third_party/python/Modules/cjkcodecs/xloadzd.h"
 /* clang-format off */
 
 static _Atomic(void *) __cp950ext_decmap_ptr;