Update changelog

Author: petk

UPGRADING.INTERNALS

@@ -299,6 +299,7 @@ PHP 7.4 INTERNALS UPGRADE NOTES
     - PHP_CHECK_CONFIGURE_OPTIONS macro has been removed. Default Autoconf's
       --enable-option-checking=fatal option can be used in the configure step
       to enable error when invalid options are used.
+    - Removed unused check and symbols HAVE_SHM_MMAP_ZERO, HAVE_SHM_MMAP_FILE.
 
   c. Windows build system changes