[NativePDB] Make tests work on x86 too

Summary:
This patch fixes the NativePDB tests to make them work from x86 command line too

Reviewers: zturner, stella.stamenova

Subscribers: aleksandr.urakov, teemperor, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D54031

llvm-svn: 345974