Fix build tool with ARMC6/ARMv8M
Fix build tool with ARMC6/ARMv8M

1. Add linking time preprocessor macro __DOMAIN_NS for non-secure build
2. For output .hex format, combine multiple .hex files (for multiple load regions) into one
   This can help for Greentea test.
3. Fix 'None' build_dir with cmse_lib.o on Greentea test

andcor02/mbed-os,c1728p9/mbed-os,mbedmicro/mbed,c1728p9/mbed-os,andcor02/mbed-os,kjbracey-arm/mbed,betzw/mbed-os,andcor02/mbed-os,mbedmicro/mbed,c1728p9/mbed-os,mbedmicro/mbed,betzw/mbed-os,andcor02/mbed-os,kjbracey-arm/mbed,mbedmicro/mbed,betzw/mbed-os,betzw/mbed-os,kjbracey-arm/mbed,andcor02/mbed-os,mbedmicro/mbed,c1728p9/mbed-os,c1728p9/mbed-os,betzw/mbed-os,betzw/mbed-os,kjbracey-arm/mbed,andcor02/mbed-os,c1728p9/mbed-os