<sys/user.h>: factor PAGE_SIZE out into <bits/page_size.h>.

If we're going to need PAGE_SIZE in other places, we don't want the
namespace pollution of pulling in all of <sys/user.h>. (The experimental
support for non-4KiB pages found an existing place -- <pthread.h> --
where we were assuming PAGE_SIZE is already available, as if
<sys/user.h> has already been included, so that was actually an existing
bug.)

Test: treehugger
Change-Id: Icd90ffbca1f2cf3645fadb2e432f6f45a4d63eb6

libc/include/bits/page_size.h

@@ -0,0 +1,40 @@
+/*
+ * Copyright (C) 2023 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+#if !defined(__BIONIC_NO_PAGE_SIZE_MACRO)
+#define PAGE_SIZE 4096
+#define PAGE_MASK (~(PAGE_SIZE - 1))
+#endif
+
+__END_DECLS

libc/include/sys/user.h

@@ -32,12 +32,9 @@
 #include <stddef.h> /* For size_t. */
 #include <stdint.h>
 
-__BEGIN_DECLS
+#include <bits/page_size.h>
 
-#if !defined(__BIONIC_NO_PAGE_SIZE_MACRO)
-#define PAGE_SIZE 4096
-#define PAGE_MASK (~(PAGE_SIZE - 1))
-#endif
+__BEGIN_DECLS
 
 #if defined(__i386__)