[MemFunctions] Add microbenchmarks for memory functions.

Memory functions (memcmp, memcpy, ...) are typically recognized by the
compiler and expanded to specific asm patterns when the size is known at
compile time.

This will help catch any regressions in expansions.

Right now we're only testing memcmp (see context in D60318).

Subscribers: mgorny, llvm-commits, gchatelet, spatel

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64082

git-svn-id: https://llvm.org/svn/llvm-project/test-suite/trunk@369707 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed