x86 needs a bit more stack to handle stack overflows.

With the interpreter, 018-stack-overflow fails when being run
command line. Through make, we're not seeing any failure because
make gives a 2GB stack space. However, running run-test in the
shell, the stack space is 8MB, and the reserved space is not enough.

Change-Id: I0da12402cdfe5ad090f34c16aa6cb8d5fbc7a3ea