[asan] Fix the coverage.cc test broken by r196939

It was failing because ASan was adding all of the following to one
function:
- dynamic alloca
- stack realignment
- inline asm

This patch avoids making the static alloca dynamic when coverage is
used.

ASan should probably not be inserting empty inline asm blobs to inhibit
duplicate tail elimination.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@196973 91177308-0d34-0410-b5e6-96231b3b80d8