arm: allow to build with DODEBUG=y
Avoids following linking error:
/usr/lib/gcc/arm-openadk-linux-uclibceabihf/5.3.0/libgcc.a(unwind-arm.o):
In function `unwind_phase2':
../w-gcc-5.3.0-1/gcc-5.3.0/libgcc/unwind-arm-common.inc:289:
undefined reference to `abort'
/usr/lib/gcc/arm-openadk-linux-uclibceabihf/5.3.0/libgcc.a(unwind-arm.o):
In function `unwind_phase2_forced':
../w-gcc-5.3.0-1/gcc-5.3.0/libgcc/unwind-arm-common.inc:346:
undefined reference to `memcpy'
collect2: error: ld returned 1 exit status