patchsha1_file: make read_info_alternates static

> read_info_alternates is not used from outside, so let's make it static.
> 
> We have to declare the function before link_alt_odb_entry instead of
> moving the code around, link_alt_odb_entry calls read_info_alternates,
> which in turn calls link_alt_odb_entry.
> 
> Signed-off-by: Stefan Beller <sbeller@google.com>
> ---
> 
>   This helps in a later refactoring (moving the object
>   store to the_repository struct), too.
>   
>   Thanks,
>   Stefan
> 
>  cache.h     | 1 -
>  sha1_file.c | 3 ++-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/cache.h b/cache.h
> index 1c69d2a05a..4109efcf24 100644
> --- a/cache.h
> +++ b/cache.h
> @@ -1551,7 +1551,6 @@ extern struct alternate_object_database {
>  	char path[FLEX_ARRAY];
>  } *alt_odb_list;
>  extern void prepare_alt_odb(void);
> -extern void read_info_alternates(const char * relative_base, int depth);
>  extern char *compute_alternate_path(const char *path, struct strbuf *err);
>  typedef int alt_odb_fn(struct alternate_object_database *, void *);
>  extern int foreach_alt_odb(alt_odb_fn, void*);
> diff --git a/sha1_file.c b/sha1_file.c
> index b60ae15f70..9186e2c6c7 100644
> --- a/sha1_file.c
> +++ b/sha1_file.c
> @@ -347,6 +347,7 @@ static int alt_odb_usable(struct strbuf *path, const char *normalized_objdir)
>   * SHA1, an extra slash for the first level indirection, and the
>   * terminating NUL.
>   */
> +static void read_info_alternates(const char * relative_base, int depth);
>  static int link_alt_odb_entry(const char *entry, const char *relative_base,
>  	int depth, const char *normalized_objdir)
>  {
> @@ -448,7 +449,7 @@ static void link_alt_odb_entries(const char *alt, int len, int sep,
>  	strbuf_release(&objdirbuf);
>  }
>  
> -void read_info_alternates(const char * relative_base, int depth)
> +static void read_info_alternates(const char * relative_base, int depth)
>  {
>  	char *map;
>  	size_t mapsz;
> -- 
> 2.14.0.rc0.3.g6c2e499285
> 

> read_info_alternates is not used from outside, so let's make it static.
> 
> We have to declare the function before link_alt_odb_entry instead of
> moving the code around, link_alt_odb_entry calls read_info_alternates,
> which in turn calls link_alt_odb_entry.
> 
> Signed-off-by: Stefan Beller <sbeller@google.com>