add PHP_CHECK_64BIT macro to be able to detect 64-bit platform in ./configure

acinclude.m4

@@ -1931,3 +1931,18 @@ dnl See ADD_EXTENSION_DEP in win32 build
 AC_DEFUN(PHP_ADD_EXTENSION_DEP, [])
 
 
+dnl PHP_CHECK_64BIT([do if 32], [do if 64])
+dnl This macro is used to detect if we're at 64-bit platform or not.
+dnl It could be useful for those external libs, that have different precompiled 
+dnl versions in different directories.
+AC_DEFUN(PHP_CHECK_64BIT,[
+  AC_CHECK_SIZEOF(int)
+  AC_MSG_CHECKING([checking if we're at 64-bit platform])
+  if test "$ac_cv_sizeof_int" = "4" ; then
+    AC_MSG_RESULT([no])
+    $1
+  else
+    AC_MSG_RESULT([yes])
+    $2
+  fi
+])