Use xattr functions from sys/xattr.h instead of attr/xattr.h (closes #12720)

sys/xattr.h is glibc while attr/xattr.h is a separate library.
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index 153ddcd..aca52e5 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -107,8 +107,8 @@
 #include <sched.h>
 #endif
 
-#ifdef HAVE_ATTR_XATTR_H
-#include <attr/xattr.h>
+#ifdef HAVE_SYS_XATTR_H
+#include <sys/xattr.h>
 #endif
 
 #if defined(__FreeBSD__) || defined(__DragonFly__) || defined(__APPLE__)
@@ -10032,7 +10032,7 @@
 }
 #endif
 
-#ifdef HAVE_ATTR_XATTR_H
+#ifdef HAVE_SYS_XATTR_H
 
 static int
 try_getxattr(const char *path, const char *name,
@@ -10408,7 +10408,7 @@
     return listxattr_common((const char *)(Py_uintptr_t)fd, wrap_flistxattr);
 }
 
-#endif /* HAVE_ATTR_XATTR_H */
+#endif /* HAVE_SYS_XATTR_H */
 
 static PyMethodDef posix_methods[] = {
     {"access",          posix_access, METH_VARARGS, posix_access__doc__},
@@ -10861,7 +10861,7 @@
 #ifdef HAVE_MKFIFOAT
     {"mkfifoat",        posix_mkfifoat, METH_VARARGS, posix_mkfifoat__doc__},
 #endif
-#ifdef HAVE_ATTR_XATTR_H
+#ifdef HAVE_SYS_XATTR_H
     {"setxattr", posix_setxattr, METH_VARARGS, posix_setxattr__doc__},
     {"lsetxattr", posix_lsetxattr, METH_VARARGS, posix_lsetxattr__doc__},
     {"fsetxattr", posix_fsetxattr, METH_VARARGS, posix_fsetxattr__doc__},
@@ -11336,7 +11336,7 @@
 #endif
 #endif
 
-#ifdef HAVE_ATTR_XATTR_H
+#ifdef HAVE_SYS_XATTR_H
     if (ins(d, "XATTR_CREATE", (long)XATTR_CREATE)) return -1;
     if (ins(d, "XATTR_REPLACE", (long)XATTR_REPLACE)) return -1;
     if (ins(d, "XATTR_SIZE_MAX", (long)XATTR_SIZE_MAX)) return -1;