add qsort_r and make qsort a wrapper around it

we make qsort a wrapper by providing a wrapper_cmp function that uses
the extra argument as a function pointer. should be optimized to a tail
call on most architectures, as long as it's built with
-fomit-frame-pointer, so the performance impact should be minimal.

to keep the git history clean, for now qsort_r is implemented in qsort.c
and qsort is implemented in qsort_nr.c.  qsort.c also received a few
trivial cleanups, including replacing (*cmp)() calls with cmp().
qsort_nr.c contains only wrapper_cmp and qsort as a qsort_r wrapper
itself.

1 files changed, 1 insertions, 0 deletions

diff --git a/include/stdlib.h b/include/stdlib.h
index b54a051f..7af86e3b 100644
--- a/include/stdlib.h
+++ b/include/stdlib.h
@@ -146,6 +146,7 @@ int clearenv(void);
 #define WCOREDUMP(s) ((s) & 0x80)
 #define WIFCONTINUED(s) ((s) == 0xffff)
 void *reallocarray (void *, size_t, size_t);
+void qsort_r (void *, size_t, size_t, int (*)(const void *, const void *, void *), void *);
 #endif
 
 #ifdef _GNU_SOURCE