Fix PHP version check for function calls with static/variable functions

Summary: D10132 improved this check by eliminating some false postives, but assumes an `n_FUNCTION_CALL` always starts with `n_SYMBOL_NAME`. This is true for `f()`, but not true for `C::m()` or `$v()`.

Test Plan: Added and ran unit tests.

Reviewers: btrahan, joshuaspence

Reviewed By: joshuaspence

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D10467