Use -fPIC on all arches; lua builds the object files into a shared lib.

[• ian]

Summary

Since the object files get built into a shared lib, using -fPIC on all arches is the right thing to do, instead of adding it to each new arch that comes along which doesn't accidentally allow non-PIC modules in shared libs.

This fixes PR 207324

Test Plan

Build- and run-tested on i386, amd64, arm, armv6.