[PGO] Fixed assertion due to mismatched memcpy size type.

Summary:
Memcpy intrinsics have size argument of any integer type, like i32 or i64.
Fixed size type along with its value when cloning the intrinsic.

Reviewers: davidxl, xur

Reviewed By: davidxl

Subscribers: mcrosier, llvm-commits

Differential Revision: https://reviews.llvm.org/D36844

llvm-svn: 311188