riscv: allow native compilation

If environment variable CROSS_COMPILE is not set, this indicates native
compilation. In this case we should not set an arbitrary value which is
not applicable for 64bit anyway.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

arch/riscv/config.mk

@@ -10,10 +10,6 @@
 # Rick Chen, Andes Technology Corporation <rick@andestech.com>
 #
 
-ifeq ($(CROSS_COMPILE),)
-CROSS_COMPILE := riscv32-unknown-linux-gnu-
-endif
-
 32bit-emul		:= elf32lriscv
 64bit-emul		:= elf64lriscv