Use standard #[cfg] directives rather than custom proc macros. Instead of having to do a bunch of custom parsing and other logic that tools often choke on, this change introduces an easy way to depend upon custom #[cfg]s provided by the libpam-sys crate.

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/build.rs	Thu Jul 03 11:03:36 2025 -0400
@@ -0,0 +1,5 @@
+use libpam_sys::pam_impl;
+
+fn main() {
+    println!("{}", pam_impl::enable_pam_impl_cfg())
+}