Summary:
A small bit that I missed when I updated the X86 backend to account for
the Win64 calling convention on non-Windows. Now we don't use dead
non-volatile registers when emitting a Win64 indirect tail call on
non-Windows.
Should fix PR23710.
Test Plan: Added test for the correct behavior based on the case I posted to PR23710.
Reviewers: rnk
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D10258
llvm-svn: 239111