Fix false positive when tag_in_malloc=0,tag_in_free=1.

Summary:
With tag_in_free=1, malloc() can not assume that the memory is untagged,
and needs to retag is to 0.

Reviewers: pcc, kcc

Subscribers: kubamracek, jfb, jdoerfert, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58158

llvm-svn: 354155