Intermittent segfault in tests

[jdm]

    Finished test [unoptimized + debuginfo] target(s) in 5m 37s

     Running `/Users/travis/build/servo/rust-mozjs/target/debug/deps/mozjs-e67ff54d0c2cfaab`

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

     Running `/Users/travis/build/servo/rust-mozjs/target/debug/deps/callback-790ad35bc706dfec`

running 1 test

test callback ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

     Running `/Users/travis/build/servo/rust-mozjs/target/debug/deps/capture_stack-0a35bd7cc59f276e`

running 1 test

test capture_stack ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

     Running `/Users/travis/build/servo/rust-mozjs/target/debug/deps/custom_auto_rooter-035f86954a24c0d4`

running 1 test

test virtual_trace_called ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

     Running `/Users/travis/build/servo/rust-mozjs/target/debug/deps/custom_auto_rooter_macro-1d9654b46023aad5`

running 1 test

test custom_auto_rooter_macro ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

     Running `/Users/travis/build/servo/rust-mozjs/target/debug/deps/enumerate-c7ae087991e1bde9`

running 1 test

test enumerate ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

     Running `/Users/travis/build/servo/rust-mozjs/target/debug/deps/evaluate-8f512ebbd5a42ea9`

running 1 test

test evaluate ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

     Running `/Users/travis/build/servo/rust-mozjs/target/debug/deps/panic-4c32e0f077cd2cbf`

running 1 test

panic-4c32e0f077cd2cbf(33169,0x700009b2c000) malloc: *** error for object 0x7fb790505c00: pointer being freed was not allocated

panic-4c32e0f077cd2cbf(33169,0x700009b2c000) malloc: *** set a breakpoint in malloc_error_break to debug

error: test failed, to rerun pass '--test panic'

Caused by:

  process didn't exit successfully: `/Users/travis/build/servo/rust-mozjs/target/debug/deps/panic-4c32e0f077cd2cbf` (signal: 6, SIGABRT: process abort signal)

The command "CCACHE=$(which ccache) RUST_BACKTRACE=1 cargo test --verbose $FEATURES" exited with 101.