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/linker/linker.cpp b/linker/linker.cpp
index 17b574f..5c26944 100644
--- a/linker/linker.cpp
+++ b/linker/linker.cpp
@@ -962,7 +962,7 @@
   }
 
   // Check if it is properly stored
-  if (entry.method != kCompressStored || (entry.offset % PAGE_SIZE) != 0) {
+  if (entry.method != kCompressStored || (entry.offset % page_size()) != 0) {
     close(fd);
     return -1;
   }
@@ -1171,7 +1171,7 @@
          "load_library(ns=%s, task=%s, flags=0x%x, realpath=%s, search_linked_namespaces=%d)",
          ns->get_name(), name, rtld_flags, realpath.c_str(), search_linked_namespaces);
 
-  if ((file_offset % PAGE_SIZE) != 0) {
+  if ((file_offset % page_size()) != 0) {
     DL_OPEN_ERR("file offset for the library \"%s\" is not page-aligned: %" PRId64, name, file_offset);
     return false;
   }