Cygwin: Make gcc-specific code in <sys/cpuset.h> compiler-agnostic

The current version of <sys/cpuset.h> cannot be compiled by Clang due to
the use of builtin versions of malloc, free, and memset.  Their presence
here was a dubious optimization anyway, so their usage has been
converted to standard library functions.

The use of __builtin_popcountl remains because Clang implements it just
like gcc does.  If/when some other compiler (Rust? Go?) runs into this
issue we can deal with specialized handling then.

The "#include <sys/cdefs>" here to define __inline can be removed since
both of the new includes sub-include it.

Addresses: https://cygwin.com/pipermail/cygwin/2023-July/253927.html
Fixes: 9cc910dd33a5 (Cygwin: Make <sys/cpuset.h> safe for c89 compilations)
Signed-off-by: Mark Geisert <mark@maxrnd.com>

winsup/cygwin/include/sys/cpuset.h

@@ -9,7 +9,8 @@ details. */
 #ifndef _SYS_CPUSET_H_
 #define _SYS_CPUSET_H_
 
-#include <sys/cdefs.h>
+#include <stdlib.h>
+#include <string.h>
 
 #ifdef __cplusplus
 extern "C" {
@@ -44,22 +45,22 @@ __cpuset_alloc_size (int num)
 static __inline cpu_set_t *
 __cpuset_alloc (int num)
 {
-  return (cpu_set_t *) __builtin_malloc (CPU_ALLOC_SIZE(num));
+  return (cpu_set_t *) malloc (CPU_ALLOC_SIZE(num));
 }
 
 #define CPU_FREE(set) __cpuset_free (set)
 static __inline void
 __cpuset_free (cpu_set_t *set)
 {
-  __builtin_free (set);
+  free (set);
 }
 
 /* These _S macros operate on dynamically-sized cpu sets of size 'siz' bytes */
 #define CPU_ZERO_S(siz, set) __cpuset_zero_s (siz, set)
 static __inline void
 __cpuset_zero_s (size_t siz, cpu_set_t *set)
 {
-  (void) __builtin_memset (set, 0, siz);
+  (void) memset (set, 0, siz);
 }
 
 #define CPU_SET_S(cpu, siz, set) __cpuset_set_s (cpu, siz, set)