Replace C++ comments with C style equivalents

* src/alloc.c (Fmake_byte_code, purecopy):
* src/bytecode.c (exec_byte_code):
* src/xdisp.c (face_at_pos): Do not use C++-style comments!

src/alloc.c

@@ -3542,7 +3542,8 @@ usage: (make-byte-code ARGLIST BYTE-CODE CONSTANTS DEPTH &optional DOCSTRING INT
 	 && FIXNATP (args[COMPILED_STACK_DEPTH])))
     error ("Invalid byte-code object");
 
-  pin_string (args[COMPILED_BYTECODE]);  // Bytecode must be immovable.
+  /* Bytecode must be immovable.  */
+  pin_string (args[COMPILED_BYTECODE]);
 
   /* We used to purecopy everything here, if purify-flag was set.  This worked
      OK for Emacs-23, but with Emacs-24's lexical binding code, it can be
@@ -5687,7 +5688,7 @@ purecopy (Lisp_Object obj)
       memcpy (vec, objp, nbytes);
       for (i = 0; i < size; i++)
 	vec->contents[i] = purecopy (vec->contents[i]);
-      // Byte code strings must be pinned.
+      /* Byte code strings must be pinned.  */
       if (COMPILEDP (obj) && size >= 2 && STRINGP (vec->contents[1])
 	  && !STRING_MULTIBYTE (vec->contents[1]))
 	pin_string (vec->contents[1]);

src/bytecode.c

@@ -789,10 +789,10 @@ exec_byte_code (Lisp_Object fun, ptrdiff_t args_template,
 	    Lisp_Object template;
 	    Lisp_Object bytecode;
 	    if (COMPILEDP (call_fun)
-		// Lexical binding only.
+		/* Lexical binding only.  */
 		&& (template = AREF (call_fun, COMPILED_ARGLIST),
 		    FIXNUMP (template))
-		// No autoloads.
+		/* No autoloads.  */
 		&& (bytecode = AREF (call_fun, COMPILED_BYTECODE),
 		    !CONSP (bytecode)))
 	      {

src/xdisp.c

@@ -4583,7 +4583,7 @@ face_at_pos (const struct it *it, enum lface_attribute_index attr_filter)
                                       &next_stop,
                                       base_face_id, false,
                                       attr_filter);
-    } // !STRINGP (it->string))
+    } /* !STRINGP (it->string) */
 }