Fix unit test broken by D27873.

Summary:
Reduce RSS size treshold in the unit test to accomodate for the smaller
ASAN quarantine size on Android (see D27873).

Reviewers: eugenis

Patch by Alex Shlyapnikov.

Subscribers: danalbert, kubabrecka, llvm-commits

Differential Revision: https://reviews.llvm.org/D28132

llvm-svn: 290643