Add sys/ucontext.h signatures for linux aarch64 glibc

Author: dtolnay

src/unix/linux_like/linux/gnu/b64/aarch64/align.rs

@@ -49,3 +49,10 @@ s! {
         pub cgroup: ::c_ulonglong,
     }
 }
+
+extern "C" {
+    pub fn getcontext(ucp: *mut ucontext_t) -> ::c_int;
+    pub fn setcontext(ucp: *const ucontext_t) -> ::c_int;
+    pub fn makecontext(ucp: *mut ucontext_t, func: extern "C" fn(), argc: ::c_int, ...);
+    pub fn swapcontext(uocp: *mut ucontext_t, ucp: *const ucontext_t) -> ::c_int;
+}