[ASan] Fix leak tests on 64-bit targets other than x86-64

Summary:
This test explicitly sets ASAN_OPTIONS=detect_leaks=1 which is only
supported on x86-64. The test is currently restricted to run only on
64-bit targets, but needs to be restricted further so it only runs on
x86-64.

Reviewers: kcc, eugenis, earthdok, samsonov

Reviewed By: samsonov

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D6189