patch 8.1.2368: using old C style comments

Problem:    Using old C style comments.
Solution:   Use // comments where appropriate.
diff --git a/src/beval.c b/src/beval.c
index 8ef8e8e..1bc31a1 100644
--- a/src/beval.c
+++ b/src/beval.c
@@ -239,13 +239,13 @@
 #endif
     static int	recursive = FALSE;
 
-    /* Don't do anything when 'ballooneval' is off, messages scrolled the
-     * windows up or we have no beval area. */
+    // Don't do anything when 'ballooneval' is off, messages scrolled the
+    // windows up or we have no beval area.
     if (!can_use_beval() || beval == NULL)
 	return;
 
-    /* Don't do this recursively.  Happens when the expression evaluation
-     * takes a long time and invokes something that checks for CTRL-C typed. */
+    // Don't do this recursively.  Happens when the expression evaluation
+    // takes a long time and invokes something that checks for CTRL-C typed.
     if (recursive)
 	return;
     recursive = TRUE;
@@ -257,7 +257,7 @@
 						    : wp->w_buffer->b_p_bexpr;
 	if (*bexpr != NUL)
 	{
-	    /* Convert window pointer to number. */
+	    // Convert window pointer to number.
 	    for (cw = firstwin; cw != wp; cw = cw->w_next)
 		++winnr;
 
@@ -285,9 +285,9 @@
 	    vim_free(result);
 	    result = eval_to_string(bexpr, NULL, TRUE);
 
-	    /* Remove one trailing newline, it is added when the result was a
-	     * list and it's hardly ever useful.  If the user really wants a
-	     * trailing newline he can add two and one remains. */
+	    // Remove one trailing newline, it is added when the result was a
+	    // list and it's hardly ever useful.  If the user really wants a
+	    // trailing newline he can add two and one remains.
 	    if (result != NULL)
 	    {
 		len = STRLEN(result);
@@ -322,4 +322,3 @@
 }
 
 #endif
-