[scudo] Add some runtime tests for the minimal runtime

Summary:
As well as some tests to ensure that various combinations of the clang command
line flags work (shared/static/minimal).

Reviewers: eugenis, alekseyshl, vitalybuka

Reviewed By: vitalybuka

Subscribers: srhines, delcypher, #sanitizers, llvm-commits

Differential Revision: https://reviews.llvm.org/D48553

llvm-svn: 335981