Add instcombine pass if sampleprofile pass is enabled.

Summary: Sample profile pass need to have instcombine pass. A related change is http://reviews.llvm.org/D17742. But we should not explicitly add dependency between to non-analysis passes. So we add the dependency here.

Reviewers: davidxl, dnovillo

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D20502

llvm-svn: 271010