net: rework errors to be cross-platform

core/net/errors_others.odin

@@ -0,0 +1,20 @@
+#+build !darwin
+#+build !linux
+#+build !freebsd
+#+build !windows
+package net
+
+@(private="file", thread_local)
+_last_error: i32
+
+_last_platform_error :: proc() -> i32 {
+	return _last_error
+}
+
+_last_platform_error_string :: proc() -> string {
+	return ""
+}
+
+_set_last_platform_error :: proc(err: i32) {
+	_last_error = err
+}