strbuf: remove global variable

As a library that only interacts with other primitives, strbuf should
not utilize the comment_line_char global variable within its
functions. Therefore, add an additional parameter for functions that use
comment_line_char and refactor callers to pass it in instead.
strbuf_stripspace() removes the skip_comments boolean and checks if
comment_line_char is a non-NUL character to determine whether to skip
comments or not.

Signed-off-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/merge.c b/builtin/merge.c
index 8da3e46..1d14767 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -879,13 +879,15 @@ static void prepare_to_commit(struct commit_list *remoteheads)
 		strbuf_addch(&msg, '\n');
 		if (cleanup_mode == COMMIT_MSG_CLEANUP_SCISSORS) {
 			wt_status_append_cut_line(&msg);
-			strbuf_commented_addf(&msg, "\n");
+			strbuf_commented_addf(&msg, comment_line_char, "\n");
 		}
-		strbuf_commented_addf(&msg, _(merge_editor_comment));
+		strbuf_commented_addf(&msg, comment_line_char,
+				      _(merge_editor_comment));
 		if (cleanup_mode == COMMIT_MSG_CLEANUP_SCISSORS)
-			strbuf_commented_addf(&msg, _(scissors_editor_comment));
+			strbuf_commented_addf(&msg, comment_line_char,
+					      _(scissors_editor_comment));
 		else
-			strbuf_commented_addf(&msg,
+			strbuf_commented_addf(&msg, comment_line_char,
 				_(no_scissors_editor_comment), comment_line_char);
 	}
 	if (signoff)