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/atexit.cpp b/libc/bionic/atexit.cpp
index 5dbf322..dae15e0 100644
--- a/libc/bionic/atexit.cpp
+++ b/libc/bionic/atexit.cpp
@@ -73,8 +73,8 @@
   // restart concurrent __cxa_finalize passes.
   uint64_t total_appends_;
 
-  static size_t page_start_of_index(size_t idx) { return PAGE_START(idx * sizeof(AtexitEntry)); }
-  static size_t page_end_of_index(size_t idx) { return PAGE_END(idx * sizeof(AtexitEntry)); }
+  static size_t page_start_of_index(size_t idx) { return page_start(idx * sizeof(AtexitEntry)); }
+  static size_t page_end_of_index(size_t idx) { return page_end(idx * sizeof(AtexitEntry)); }
 
   // Recompact the array if it will save at least one page of memory at the end.
   bool needs_recompaction() const {
@@ -167,7 +167,7 @@
 // than one.
 bool AtexitArray::next_capacity(size_t capacity, size_t* result) {
   if (capacity == 0) {
-    *result = PAGE_END(sizeof(AtexitEntry)) / sizeof(AtexitEntry);
+    *result = page_end(sizeof(AtexitEntry)) / sizeof(AtexitEntry);
     return true;
   }
   size_t num_bytes;