ARC: Don't pre-define CROSS_COMPILE

Even though arc-linux- prefix is used in ARC prebuilt tools and
in Buildroot there're other options like Linux distro cross-tools
etc where prefix is different so let's not rely on this default.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>

arch/arc/config.mk

@@ -9,21 +9,15 @@ CONFIG_SYS_BIG_ENDIAN = 1
 endif
 
 ifdef CONFIG_SYS_LITTLE_ENDIAN
-ARC_CROSS_COMPILE := arc-linux-
 PLATFORM_LDFLAGS += -EL
 PLATFORM_CPPFLAGS += -mlittle-endian
 endif
 
 ifdef CONFIG_SYS_BIG_ENDIAN
-ARC_CROSS_COMPILE := arceb-linux-
 PLATFORM_LDFLAGS += -EB
 PLATFORM_CPPFLAGS += -mbig-endian
 endif
 
-ifeq ($(CROSS_COMPILE),)
-CROSS_COMPILE := $(ARC_CROSS_COMPILE)
-endif
-
 ifdef CONFIG_ARC_MMU_VER
 CONFIG_MMU = 1
 endif