fix TOOLPREFIX

Makefile

@@ -43,10 +43,7 @@ TOOLPREFIX := $(shell if riscv64-unknown-elf-objdump -i 2>&1 | grep 'elf64-big'
 	then echo 'riscv64-unknown-elf-'; \
 	elif riscv64-linux-gnu-objdump -i 2>&1 | grep 'elf64-big' >/dev/null 2>&1; \
 	then echo 'riscv64-linux-gnu-'; \
-	else echo "***" 1>&2; \
-	echo "*** Error: Couldn't find an riscv64 version of GCC/binutils." 1>&2; \
-	echo "*** To turn off this error, run 'gmake TOOLPREFIX= ...'." 1>&2; \
-	echo "***" 1>&2; exit 1; fi)
+	else echo "no-toolchain-found-" fi)
 endif
 
 QEMU = qemu-system-riscv64