ThinLTO: Fix assembler to emit alwaysInline in the summary

Summary: The earlier commit (https://reviews.llvm.org/D70014) missed this one : If Always_Inline happens to be the only entry in FuncFlags, then the assembler will not print it in the summary.

Patch by Bharathi Seshadri <bseshadr@cisco.com>

Reviewers: tejohnson

Reviewed By: tejohnson

Subscribers: mehdi_amini, inglorion, hiraditya, steven_wu, dexonsmith, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D70323