Export the preload_index() function

The purpose of this function is to stat() the files listed in the index
in a multi-threaded fashion. It is called directly after reading the
index in the read_index_preloaded() function.

However, in some cases we may want to separate the index reading from
the preloading step, e.g. in builtin/add.c, where we need to load the
index before we parse the pathspecs (which needs to error out if one of
the pathspecs refers to a path within a submodule, for which the index
must have been read already), and only then will we want to preload,
possibly limited by the just-parsed pathspecs.

So let's just export that function to allow calling it separately.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

cache.h

@@ -659,6 +659,7 @@ extern int daemonize(void);
 /* Initialize and use the cache information */
 struct lock_file;
 extern int read_index(struct index_state *);
+extern void preload_index(struct index_state *, const struct pathspec *pathspec);
 extern int read_index_preload(struct index_state *, const struct pathspec *pathspec);
 extern int do_read_index(struct index_state *istate, const char *path,
 			 int must_exist); /* for testting only! */

preload-index.c

@@ -7,8 +7,7 @@
 #include "fsmonitor.h"
 
 #ifdef NO_PTHREADS
-static void preload_index(struct index_state *index,
-			  const struct pathspec *pathspec)
+void preload_index(struct index_state *index, const struct pathspec *pathspec)
 {
 	; /* nothing */
 }
@@ -73,8 +72,7 @@ static void *preload_thread(void *_data)
 	return NULL;
 }
 
-static void preload_index(struct index_state *index,
-			  const struct pathspec *pathspec)
+void preload_index(struct index_state *index, const struct pathspec *pathspec)
 {
 	int threads, i, work, offset;
 	struct thread_data data[MAX_PARALLEL];