Remove PAGE_SIZE call sites.

To enable experiments with non-4KiB page sizes, introduce
an inline page_size() function that will either return the runtime
page size (if PAGE_SIZE is not 4096) or a constant 4096 (elsewhere).
This should ensure that there are no changes to the generated code on
unaffected platforms.

Test: source build/envsetup.sh
      lunch aosp_cf_arm64_16k_phone-userdebug
      m -j32 installclean
      m -j32
Test: launch_cvd \
  -kernel_path /path/to/out/android14-5.15/dist/Image \
  -initramfs_path /path/to/out/android14-5.15/dist/initramfs.img \
  -userdata_format=ext4
Bug: 277272383
Bug: 230790254
Change-Id: Ic0ed98b67f7c6b845804b90a4e16649f2fc94028
diff --git a/libc/bionic/getpagesize.cpp b/libc/bionic/getpagesize.cpp
index 3a59900..da97633 100644
--- a/libc/bionic/getpagesize.cpp
+++ b/libc/bionic/getpagesize.cpp
@@ -27,9 +27,10 @@
  */
 
 #include <unistd.h>
+#include "platform/bionic/page.h"
 
 // Portable code should use sysconf(_SC_PAGE_SIZE) directly instead.
 int getpagesize() {
   // We dont use sysconf(3) here because that drags in stdio, which makes static binaries fat.
-  return PAGE_SIZE;
+  return page_size();
 }