fix configure check to require at least V8 6.9

config.m4

@@ -140,14 +140,8 @@ int main ()
     set $ac_cv_v8_version
     IFS=$ac_IFS
     V8_API_VERSION=`expr [$]1 \* 1000000 + [$]2 \* 1000 + [$]3`
-    if test "$V8_API_VERSION" -lt 4006076 ; then
-       AC_MSG_ERROR([libv8 must be version 4.6.76 or greater])
-    fi
-    if test "$V8_API_VERSION" -lt 6004388 ; then
-       AC_MSG_WARN([libv8 prior to 6.4.388.18 is missing speculative execution mitigations])
-    fi
-    if test "$V8_API_VERSION" -ge 6005000 -a "$V8_API_VERSION" -lt 6005143 ; then
-       AC_MSG_WARN([libv8 6.5.x prior to 6.5.143 is missing speculative execution mitigations])
+    if test "$V8_API_VERSION" -lt 6009000 ; then
+       AC_MSG_ERROR([libv8 must be version 6.9 or greater])
     fi
     AC_DEFINE_UNQUOTED([PHP_V8_API_VERSION], $V8_API_VERSION, [ ])
     AC_DEFINE_UNQUOTED([PHP_V8_VERSION], "$ac_cv_v8_version", [ ])