Make clock setup functions weak symbols in ARMv8-M ports.
Update Cortex-M33 ports to use an interrupt mask in place of globally disabling interrupts, as per the other Cortex-M ports.
IAR produces some warnings which can not be fixed in the source code because
then other compilers start generating warnings. We suppressed those warnings
in the project file before. This change moves the warning suppression from
project files to portmacro.h.
