Incorrect syntax for multi-line command
It turns out that
@+failed_builds=0; \
@+for ARCH in ${CROSS_COMPILER_TARGET_ARCHS}; do \
umask 002; echo MAKING ARCH $$ARCH; ${MAKE} -f ${USERMAKEFILE} T_A=$$ARCH $@ || ((failed_builds++)); \
done; \
@+((failed_builds == 0))
is not correct for multi-line commands in a make recipe. The @+
s on the later lines need to be gone.