[libc] Fix pthread_create_test for 32 bit systems (#66564)

The test tries to set the guard_size and stack_size of a thread to
SIZE_MAX / 4, which is a huge value in 64-bit systems but 1GB in 32-bit
ones.

We increase the size to 3 * (SIZE_MAX / 4) so it can also fail in 32-bit 
systems.