[scudo][standalone] Fix tests makefile
A missing STATIC entailed some annoying to debug failures wrt 32 vs 64
binaries. Additionally I noticed I was using the wrong variable (the Scudo
one as opposed to the Scudo Standalone one).
See https://reviews.llvm.org/D58184#1412417 and below for discussion.
Reviewers: vitalybuka, eugenis, brzycki
Reviewed By: vitalybuka, brzycki
Subscribers: mgorny, delcypher, #sanitizers, llvm-commits
Tags: #llvm, #sanitizers
Differential Revision: https://reviews.llvm.org/D58794