Merge branch 'eb/no-pthreads'

Allow us build with NO_PTHREADS=NoThanks compilation option.

* eb/no-pthreads:
  Handle atexit list internaly for unthreaded builds
  pack-objects: set number of threads before checking and warning
  index-pack: fix compilation with NO_PTHREADS

git-compat-util.h

@@ -596,6 +596,11 @@ int inet_pton(int af, const char *src, void *dst);
 const char *inet_ntop(int af, const void *src, char *dst, size_t size);
 #endif
 
+#ifdef NO_PTHREADS
+#define atexit git_atexit
+extern int git_atexit(void (*handler)(void));
+#endif
+
 extern void release_pack_memory(size_t);
 
 typedef void (*try_to_free_t)(size_t);