[IR] Use Min behavior for module flag "PIC Level"

[IR] Use Min behavior for module flag "PIC Level"

Using Max for both "PIC Level" and "PIE Level" is inconsistent. PIC imposes less
restriction while PIE imposes more restriction. The result generally
picks the more restrictive behavior: Min for PIC.

This choice matches `ld -r`: a non-pic object and a pic object merge into a
result which should be treated as non-pic.

To allow linking "PIC Level" using Error/Max from old bitcode files, upgrade
Error/Max to Min.

Reviewed By: tejohnson

Differential Revision: https://reviews.llvm.org/D130531