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

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

third_party/git/t/helper/test-mktemp.c

@@ -0,0 +1,15 @@
+/*
+ * test-mktemp.c: code to exercise the creation of temporary files
+ */
+#include "test-tool.h"
+#include "git-compat-util.h"
+
+int cmd__mktemp(int argc, const char **argv)
+{
+	if (argc != 2)
+		usage("Expected 1 parameter defining the temporary file template");
+
+	xmkstemp(xstrdup(argv[1]));
+
+	return 0;
+}