Temporarily set CHPL_RT_CALL_STACK_SIZE=2M for linux32 builds

Qthreads preallocates stacks for 128 threads up front and our large stack size
of 8M means we have over 1GB allocated right away which causes segfaults for
linux32. This is meant as a temporary measure so that we can get some testing
in for qthreads still.
Merge pull request #218 from ronawho/qthreads-as-default

Temporarily set CHPL_RT_CALL_STACK_SIZE=2M for linux32 builds

Qthreads preallocates stacks for 128 threads up front and our large stack size
of 8M means we have over 1GB allocated right away which causes segfaults for
linux32. This is meant as a temporary measure so that we can get some testing
in for qthreads still.