Reapply fix PR23384 (part 3 of 3) r304824 (was reverted in r305720).

The root cause of reverting was fixed - PR33514.

Summary:
The patch makes instruction count the highest priority for
 LSR solution for X86 (previously registers had highest priority).

Reviewers: qcolombet

Differential Revision: http://reviews.llvm.org/D30562

From: Evgeny Stupachenko <evstupac@gmail.com>
                         <evgeny.v.stupachenko@intel.com>
llvm-svn: 310289