builtin rebase: support `ignore-whitespace` option

This commit adds support for the `--ignore-whitespace` option
of the rebase command. This option is simply passed to the
`--am` backend.

Signed-off-by: Pratik Karki <predatoramigo@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/rebase.c

@@ -527,6 +527,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		ACTION_SHOW_CURRENT_PATCH,
 	} action = NO_ACTION;
 	int committer_date_is_author_date = 0;
+	int ignore_whitespace = 0;
 	struct option builtin_rebase_options[] = {
 		OPT_STRING(0, "onto", &options.onto_name,
 			   N_("revision"),
@@ -542,6 +543,8 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		{OPTION_NEGBIT, 'n', "no-stat", &options.flags, NULL,
 			N_("do not show diffstat of what changed upstream"),
 			PARSE_OPT_NOARG, NULL, REBASE_DIFFSTAT },
+		OPT_BOOL(0, "ignore-whitespace", &ignore_whitespace,
+			 N_("passed to 'git apply'")),
 		OPT_BOOL(0, "signoff", &options.signoff,
 			 N_("add a Signed-off-by: line to each commit")),
 		OPT_BOOL(0, "committer-date-is-author-date",
@@ -773,6 +776,9 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		options.flags |= REBASE_FORCE;
 	}
 
+	if (ignore_whitespace)
+		strbuf_addstr(&options.git_am_opt, " --ignore-whitespace");
+
 	switch (options.type) {
 	case REBASE_MERGE:
 	case REBASE_INTERACTIVE: