merge(third_party/git): Merge squashed git subtree at v2.23.0

Merge commit '1b593e1ea4' as 'third_party/git'

third_party/git/builtin/merge-ours.c

@@ -0,0 +1,33 @@
+/*
+ * Implementation of git-merge-ours.sh as builtin
+ *
+ * Copyright (c) 2007 Thomas Harning Jr
+ * Original:
+ * Original Copyright (c) 2005 Junio C Hamano
+ *
+ * Pretend we resolved the heads, but declare our tree trumps everybody else.
+ */
+#define USE_THE_INDEX_COMPATIBILITY_MACROS
+#include "git-compat-util.h"
+#include "builtin.h"
+#include "diff.h"
+
+static const char builtin_merge_ours_usage[] =
+	"git merge-ours <base>... -- HEAD <remote>...";
+
+int cmd_merge_ours(int argc, const char **argv, const char *prefix)
+{
+	if (argc == 2 && !strcmp(argv[1], "-h"))
+		usage(builtin_merge_ours_usage);
+
+	/*
+	 * The contents of the current index becomes the tree we
+	 * commit.  The index must match HEAD, or this merge cannot go
+	 * through.
+	 */
+	if (read_cache() < 0)
+		die_errno("read_cache failed");
+	if (index_differs_from(the_repository, "HEAD", NULL, 0))
+		exit(2);
+	exit(0);
+}