[HackC] some keywords are case sensitive

[fredemmott]

Reported by fwaggle on Freenode IRC

HHVM Version

3.26.0

Operating System and Version

MacOS High Sierra

Standalone code, or other way to reproduce the problem

<?php

Function hello() {
echo 'hi';
}

hello();

Expected result

hi (this is the output if you replace Function with function, or if you disable hackc)

Actual result

$ hhvm test.php

Fatal error: Uncaught Error: A semicolon (';') is expected here. in /private/tmp/test.php:3
Stack trace:
#0 {main}

[fredemmott]

We have tests for these in hphp/test/slow/parser/keyword_case/ but they're all skipping if __COMPILER_FRONTEND__ === 'hackc'