[ThinLTO] Refine fix to avoid renaming of uses in inline assembly.

[ThinLTO] Refine fix to avoid renaming of uses in inline assembly.

Summary:
Refine the workaround from r266877 that attempts to prevent
renaming of locals in inline assembly, so that in addition to looking
for a llvm.used local value, that there is at least one inline assembly
call in the module. Otherwise, debug functions added to the llvm.used
can block importing/exporting unnecessarily.

Reviewers: joker.eph

Subscribers: llvm-commits, joker.eph

Differential Revision: http://reviews.llvm.org/D19573

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@267717 91177308-0d34-0410-b5e6-96231b3b80d8