ARMv7-M: Fix logic that determines if there is a pending signal action before scheduling the next signal action.  Both the test and the scheduling action need to be atomic

init hw, draft

Sim target on Cygwin64: Modern Cygwin X86_64 machines follow the Microsoft ABI for parameter passing.  The older,inux System 5 ABI will not work on X86_64-based Cygwin machines.  With this change, the simulator agains works with the newer Cygwin64 platform

Simulation: Newer versions of Cygwin tools do not seem to pre-pend symbol names with underscore character

add swo for stm32F4xxx

stm32f74xx75xx_irq.h: STM32_IRQ_SAI2 is not defined but STM32_IRQ_SAI1 is defined twice.  Noted by Vlad Chiorean

SAMA5D: Move common configuration logic from sam_lowputc.c and sam_serial.c to new sam_config.h.  Make room in the architecture for forthcoming Flexcom USARTs