mmap-alloc: Tests fail on Mac Travis CI

[joshlf]

On Mac Travis CI, we're getting odd test failures for the mmap-alloc crate with a SIGBUS in the test_map_panic_too_large test.

For example, this build:

Running `/Users/travis/build/ezrosent/allocators-rs/mmap-alloc/target/debug/deps/mmap_alloc-78657eb3ad591fbe`
running 11 tests
test tests::bench_large_map ... ignored
test tests::test_commit ... ok
test tests::test_map ... ok
test tests::test_map_non_windows ... ok
test tests::test_map_panic_too_large ... error: process didn't exit successfully: `/Users/travis/build/ezrosent/allocators-rs/mmap-alloc/target/debug/deps/mmap_alloc-78657eb3ad591fbe` (signal: 10, SIGBUS: access to undefined memory)

This issue has not come up on master yet, but is currently only present on the tls branch (PR #85), which is particularly odd since no changes to mmap-alloc are made on that branch.

[joshlf]

This issue has come up in #122 as well.

[joshlf]

OK, it looks like the issue is just that mmap-alloc tests are failing in general on Travis Mac, not just test_map_panic_too_large in particular. I'll update the PR to disable on Mac entirely.

[joshlf]

Looks like this might be the culprit: rust-lang/rust#45866. After it lands in nightly tomorrow, we should re-enable these tests to see if that change fixes it.