https://salsa.debian.org/lua-team/lua5.1/-/blob/master/debian/patches/0003-extern_C.patch

From: "John V. Belmonte" <jbelmonte@debian.org>
Date: Tue, 26 Aug 2014 16:20:49 +0200
Subject: extern_C

--- a/src/luaconf.h.in
+++ b/src/luaconf.h.in
@@ -168,7 +168,11 @@
 
 #else
 
+#ifdef __cplusplus
+#define LUA_API		extern "C"
+#else
 #define LUA_API		extern
+#endif
 
 #endif