bionic: Use getauxval(AT_PAGESZ) for page agnostic targets

When the C flag -D__BIONIC_NO_PAGE_SIZE_MACRO is defined,
the function getauxval(AT_PAGESZ) will be called instead of
using the PAGE_SIZE macro for the arm64 architectures.

Bug: 277272383
Bug: 289419664

Test: source build/envsetup.sh
      lunch aosp_raven_pgagnostic_64-userdebug
      m

      source build/envsetup.sh
      lunch aosp_cf_x86_64_phone
      m

Change-Id: Ie904ee5601365abbcf93ee371922a351844eccff
diff --git a/libc/platform/bionic/page.h b/libc/platform/bionic/page.h
index 5f4bb6f..a75b3ac 100644
--- a/libc/platform/bionic/page.h
+++ b/libc/platform/bionic/page.h
@@ -24,16 +24,11 @@
 #include <sys/user.h>
 
 inline size_t page_size() {
-  /*
-   * PAGE_SIZE defines the maximum supported page size. Since 4096 is the
-   * minimum supported page size we can just let it be constant folded if it's
-   * also the maximum.
-   */
-#if PAGE_SIZE == 4096
+#if defined(PAGE_SIZE)
   return PAGE_SIZE;
 #else
-  static size_t size = getauxval(AT_PAGESZ);
-  return size;
+  static const size_t page_size = getauxval(PAGE_SIZE);
+  return page_size;
 #endif
 }