Xtensa ESP32:  Corrects a problem with dispatching to signal handlers:  Cannot vector directly to the signal handling function as in other ABIs under the Xtensa Window ABI.  In that case, we need to go through a tiny hook when performs the correct window call (call4) otherwise registers will be scrambled in the signal handler

Xtensa ESP32: Some fixes from integration of ostest configuration.  Almost works: There are some assertions in xtensa_sigdeliver()

Xtensa ESP32:  Clock frequency is different if running from IRAM or is booting from FLASH.   This is a booltloader issue.

Support PWM_PULSECOUNT feature for TI tiva

Xtensa ESP32: Need to spill registers to memory as the last dying action before switching to a new thread.

Fix context save logic when called in window ABI configuration. Add an IDLE stack.  Don't depend on the mystery stack received from the bootloader.