Set runtime stack size to 2M for 32bit platform in smoke test.

Default runtime stack size is 8M, but with qthreads tasking layer, this uses a
lot more memory than we want (because it pre-allocates 128 stacks at 8M each).

requested by @ronawho
Merge pull request #230 from thomasvandoren/reduce-stack-size-for-32bit-smoke-test

Set runtime stack size to 2M for 32bit platform in smoke test. (temporary workaround)

Default runtime stack size is 8M, but with qthreads tasking layer, this uses a
lot more memory than we want (because it pre-allocates 128 stacks at 8M each).

requested by @ronawho