[ASan] Disable allocator_oom_test.cc on s390

Summary:
ASan shadow memory on s390 is larger than other configurations, let's
disable this test for now (will revisit it later).

Reviewers: eugenis

Subscribers: kubamracek, llvm-commits

Differential Revision: https://reviews.llvm.org/D34414

llvm-svn: 305822