C++(C99)-style comments in git.git

> Avoid C++ style comments, that are not allowed in C89.
>
> Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com>
> ---
>  reftable/stack_test.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/reftable/stack_test.c b/reftable/stack_test.c
> index 7a4641ab60..f907215d3c 100644
> --- a/reftable/stack_test.c
> +++ b/reftable/stack_test.c
> @@ -46,8 +46,10 @@ static int count_dir_entries(const char *dirname)
>  	return len;
>  }
>  
> -// Work linenumber into the tempdir, so we can see which tests forget to
> -// cleanup.
> +/*
> + * Work linenumber into the tempdir, so we can see which tests forget to
> + * cleanup.
> + */
>  static char *get_tmp_template(int linenumber)
>  {
>  	const char *tmp = getenv("TMPDIR");
> @@ -861,7 +863,7 @@ static void test_reftable_stack_compaction_concurrent(void)
>  
>  static void unclean_stack_close(struct reftable_stack *st)
>  {
> -	// break abstraction boundary to simulate unclean shutdown.
> +	/* break abstraction boundary to simulate unclean shutdown */
>  	int i = 0;
>  	for (; i < st->readers_len; i++) {
>  		reftable_reader_free(st->readers[i]);