f32x2 vector arithmetic ops fail on x86_64-apple-darwin

[gnzlbg]

I cannot reproduce this locally but the following two tests fail on x86_64-apple-darwin on travis:

---- v64::f32x2_ops_scalar_arith::ops_scalar_arithmetic stdout ----
thread 'v64::f32x2_ops_scalar_arith::ops_scalar_arithmetic' panicked at 'assertion failed: `(left == right)`
  left: `f32x2(NaN, 0.0)`,
 right: `f32x2(0.0, 0.0)`', src/v64.rs:43:1
---- v64::f32x2_ops_vector_arith::ops_vector_arithmetic stdout ----
thread 'v64::f32x2_ops_vector_arith::ops_vector_arithmetic' panicked at 'assertion failed: `(left == right)`
  left: `f32x2(NaN, 0.0)`,
 right: `f32x2(0.0, 0.0)`', src/v64.rs:43:1
failures:
    v64::f32x2_ops_scalar_arith::ops_scalar_arithmetic
    v64::f32x2_ops_vector_arith::ops_vector_arithmetic

[gnzlbg]

Update: after disabling the AVX1 tests, these started failing with illegal instruction on travis. It appears that the travis apple build bots do not support AVX2. So now that AVX1 is disabled, I've disabled AVX2 testing for apple builds, and tests pass again.

We should re-enable AVX1 and figure out why this was failing.