libroot/stdlib: Add qsort_r.

It's in POSIX-2024. Remove the libgnu implementation and just import
the changes from latest FreeBSD (dc36d6f9bb1753f3) instead.

While at it, put the non-standard sort functions behind
_DEFAULT_SOURCE.

headers/compatibility/gnu/stdlib.h

@@ -1,37 +0,0 @@
-/*
- * Copyright 2020 Haiku, Inc. All rights reserved.
- * Distributed under the terms of the MIT License.
- *
- * Authors:
- *		Isaac Turner, [email protected]
- *		Jacob Secunda, [email protected]
- */
-#ifndef _GNU_STDLIB_H_
-#define _GNU_STDLIB_H_
-
-
-#include_next <stdlib.h>
-#include <features.h>
-
-
-#ifdef _DEFAULT_SOURCE
-
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
-typedef int (*_compare_function_qsort_r)(const void*, const void*, void*);
-
-extern void qsort_r(void* base, size_t numElements, size_t sizeOfElement,
-	_compare_function_qsort_r, void* cookie);
-
-#ifdef __cplusplus
-}
-#endif
-
-
-#endif /* _DEFAULT_SOURCE */
-
-
-#endif /* _GNU_STDLIB_H_ */

headers/posix/stdlib.h

@@ -120,19 +120,25 @@ extern void		lcong48(unsigned short int param[7]);
 
 /* search and sort functions */
 typedef int (*_compare_function)(const void *, const void *);
+typedef int (*_compare_function_qsort_r)(const void*, const void*, void*);
 
 extern void		*bsearch(const void *key, const void *base, size_t numElements,
 					size_t sizeOfElement, _compare_function);
+extern void		qsort(void *base, size_t numElements, size_t sizeOfElement,
+					_compare_function);
+extern void		qsort_r(void* base, size_t numElements, size_t sizeOfElement,
+					_compare_function_qsort_r, void* cookie);
+
+#ifdef _DEFAULT_SOURCE
 extern int		heapsort(void *base, size_t numElements, size_t sizeOfElement,
 					_compare_function);
 extern int		mergesort(void *base, size_t numElements, size_t sizeOfElement,
 					_compare_function);
-extern void		qsort(void *base, size_t numElements, size_t sizeOfElement,
-					_compare_function);
 extern int		radixsort(u_char const **base, int numElements,
 					u_char const *table, u_int endByte);
 extern int		sradixsort(u_char const **base, int numElements,
 					u_char const *table, u_int endByte);
+#endif
 
 /* misc math functions */
 extern int		abs(int number);