[Inlining] Introduce -enable-npm-pgo-inline-deferral

Summary:
Experiments show that inline deferral past pre-inlining slightly
pessimizes the performance.

This patch introduces an option to control inline deferral during PGO.
The option defaults to true for now (that is, NFC).

Reviewers: davidxl

Reviewed By: davidxl

Subscribers: eraman, hiraditya, haicheng, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D80776