Compatibility with gcc 13 (pre-C23), see:
https://codeberg.org/jengelh/pam_mount/commit/64dfcc87ccb6f7b0243b206524f7ea9aa9c59bc8

diff --git a/src/pam_mount.h b/src/pam_mount.h
index 61395f7..f547d8c 100644
--- a/src/pam_mount.h
+++ b/src/pam_mount.h
@@ -14,6 +14,9 @@
 #else
 #	define EXPORT_SYMBOL
 #endif
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ < 202300L
+#	define nullptr NULL
+#endif
 
 #define sizeof_z(x) (sizeof(x) - 1)