Rename Borland C to C++ and update sLang

Rename db/LX/compiler_Borland_C.4.sg to db/LX/compiler_Borland_C++.4.sg and update the detect() function to set sLang from "C/C++" to "C++". This adjusts the file/name to explicitly represent the C++ compiler and aligns the language identifier accordingly; no other functional changes.

db/LX/compiler_Borland_C++.4.sg

@@ -13,7 +13,7 @@ function detect() {
 
     bDetected = bDetected || Boolean(sVersion) || Boolean(sOptions);
 
-    sLang = "C/C++";
+    sLang = "C++";
 
     return result();
 }