[GVNHoist] Call isGuaranteedToTransferExecutionToSuccessor on each instruction

w.r.t. https://bugs.llvm.org/show_bug.cgi?id=32153
The consensus seems to be isGuaranteedToTransferExecutionToSuccessor should be called for each function.

Patch by Aditya Kumar

Differential Revision: https://reviews.llvm.org/D31035

llvm-svn: 299882