[compiler-rt] Fix broken interception unittest

Summary:
This patch is fixing a broken unittest which make the win64 bot failing.

The bug was introduce here:
  https://reviews.llvm.org/D23046

The interception code is not the same in 32-bit and in 64-bit.
The added unittest can only be patched on 32-bits.

Reviewers: rnk

Subscribers: llvm-commits, chrisha

Differential Revision: https://reviews.llvm.org/D23099

llvm-svn: 277560