CONFIG_ARM_TOOLCHAIN_GNU_EABI build got broken when -mthumb option was moved
from ARCHCPUFLAGS to ARCHOPTIMIZATION variable:
arm-none-eabi-ld: error: .../build/nuttx/nuttx uses VFP register arguments, /usr/lib/gcc/arm-none-eabi/5.4.1/libgcc.a(_fixunsdfdi.o) does not
arm-none-eabi-ld: failed to merge target specific data of file /usr/lib/gcc/arm-none-eabi/5.4.1/libgcc.a(_fixunsdfdi.o)
arm-none-eabi-ld: error: .../build/nuttx/nuttx uses VFP register arguments, /usr/lib/gcc/arm-none-eabi/5.4.1/libgcc.a(_udivmoddi4.o) does not
arm-none-eabi-ld: failed to merge target specific data of file /usr/lib/gcc/arm-none-eabi/5.4.1/libgcc.a(_udivmoddi4.o)