Change: increasing the default stack size to 160k.

Change: increasing the default stack size to 160k.

This change allows EarleyBoyer benchmark from
arewefastyet/benchmarks/v8-v7 to pass with default settings.

Previous commit 5e9a6d5 (v0.7.9) reduced the stack size to prevent stack
overflow when compiling with -O0 in computed goto mode, where native
stack frames for njs_vmcode_interpreter() consume ~80KB each. To address
this, we now set a lower maximum stack size specifically for unit tests.

This fixes #939 issue on Github.