Merge branch 'js/diff-rename-force-stable-sort'

The rename detection logic sorts a list of rename source candidates
by similarity to pick the best candidate, which means that a tie
between sources with the same similarity is broken by the original
location in the original candidate list (which is sorted by path).
Force the sorting by similarity done with a stable sort, which is
not promised by system supplied qsort(3), to ensure consistent
results across platforms.

* js/diff-rename-force-stable-sort:
  diffcore_rename(): use a stable sort
  Move git_sort(), a stable sort, into into libgit.a

git-compat-util.h

@@ -1092,10 +1092,10 @@ static inline int strtol_i(char const *s, int base, int *result)
 	return 0;
 }
 
+void git_stable_qsort(void *base, size_t nmemb, size_t size,
+		      int(*compar)(const void *, const void *));
 #ifdef INTERNAL_QSORT
-void git_qsort(void *base, size_t nmemb, size_t size,
-	       int(*compar)(const void *, const void *));
-#define qsort git_qsort
+#define qsort git_stable_qsort
 #endif
 
 #define QSORT(base, n, compar) sane_qsort((base), (n), sizeof(*(base)), compar)
@@ -1106,6 +1106,9 @@ static inline void sane_qsort(void *base, size_t nmemb, size_t size,
 		qsort(base, nmemb, size, compar);
 }
 
+#define STABLE_QSORT(base, n, compar) \
+	git_stable_qsort((base), (n), sizeof(*(base)), compar)
+
 #ifndef HAVE_ISO_QSORT_S
 int git_qsort_s(void *base, size_t nmemb, size_t size,
 		int (*compar)(const void *, const void *, void *), void *ctx);