Add new os_specific_*.odin files

core/runtime/os_specific_any.odin

@@ -0,0 +1,17 @@
+//+build !freestanding
+//+build !windows
+package runtime
+
+import "core:os"
+
+// TODO(bill): reimplement `os.write` so that it does not rely on package os
+// NOTE: Use os_specific_linux.odin, os_specific_darwin.odin, etc
+os_write :: proc "contextless" (data: []byte) -> (int, _OS_Errno) {
+	context = default_context();
+	n, err := os.write(os.stderr, data);
+	return int(n), _OS_Errno(err);
+}
+
+current_thread_id :: proc "contextless" () -> int {
+	return os.current_thread_id();
+}