[libc] Fix some tests on NVPTX due to insufficient stack size

A few of these tests were disabled due to failing on NVPTX. After
looking into it the vast majority of these cases were due to
insufficient stack memory. This can be worked around by increasing the
stack size in the loader or by reducing the memory usage in the case of
large string constants.

Reviewed By: tra

Differential Revision: https://reviews.llvm.org/D152583