Change shm_open() calling ABI on aarch64 Darwin (#43516)

Beacuse `shm_open()` is a variadic function, if we don't declare it as
such, the kernel receives trash as the `permissions` value, which
occasionally results in errors when creating shared memory segments.
This did not happen on `x86_64` because the calling convention doesn't
change so much between variadic and non-vadiadic functions.

Author: staticfloat

stdlib/SharedArrays/src/SharedArrays.jl

@@ -693,9 +693,15 @@ function _shm_mmap_array(T, dims, shm_seg_name, mode)
 end
 
 shm_unlink(shm_seg_name) = ccall(:shm_unlink, Cint, (Cstring,), shm_seg_name)
-shm_open(shm_seg_name, oflags, permissions) = ccall(:shm_open, Cint,
-    (Cstring, Cint, Base.Cmode_t), shm_seg_name, oflags, permissions)
-
+function shm_open(shm_seg_name, oflags, permissions)
+    # On macOS, `shm_open()` is a variadic function, so to properly match
+    # calling ABI, we must declare our arguments as variadic as well.
+    @static if Sys.isapple()
+        return ccall(:shm_open, Cint, (Cstring, Cint, Base.Cmode_t...), shm_seg_name, oflags, permissions)
+    else
+        return ccall(:shm_open, Cint, (Cstring, Cint, Base.Cmode_t), shm_seg_name, oflags, permissions)
+    end
+end
 end # os-test
 
 end # module