[libomptarget][nfc] Move hostcall required test to rtl

[libomptarget][nfc] Move hostcall required test to rtl

Remove a global, fix minor race. First of N patches to bring up hostcall.

Reviewed By: JonChesterfield

Differential Revision: https://reviews.llvm.org/D103058

GitOrigin-RevId: df005fa364ae3914231f98f80acc120fcf782c26
2 files changed