Update FlexLinker.h to current version of flex.

This file is copied here and has become out of sync w/ flex.

Bug: 31194194
Test: build and boot device
Test: atest CtsRenderscriptTestCases
Total Tests       : 744
PASSED            : 744
FAILED            : 0

Test: atest CtsRenderscriptTestCases -it -- --abi=armeabi-v7a
Total Tests       : 744
PASSED            : 744
FAILED            : 0

Change-Id: Ib8102727724d87725992c97abc29ab9e06ec4ee1