Remove debug info when hoisting instruction from then/else branch.

Summary: The hoisted instruction is executed speculatively. It could affect the debugging experience as user would see gdb go into code that may not be expected to execute. It will also affect sample profile accuracy by assigning incorrect frequency to source within then/else branch.

Reviewers: davidxl, dblaikie, chandlerc, kcc, echristo

Subscribers: mehdi_amini, probinson, eric_niebler, andreadb, llvm-commits

Differential Revision: https://reviews.llvm.org/D24164

llvm-svn: 280995