[Libomptarget] Reduce shared memory stack size to 512 and a message when it is exceeded

Reduces the shared memory size used for globalization to 512 bytes from
2048 to reduce the pressure on shared memory. This patch ado adds a
debug mesage to indicate when the shared memory was insufficient.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D118625