binutils: fix build with external toolchains on avr32

Fixes http://autobuild.buildroot.org/results/7f0545a7c824bf0523ab3506db83f7f5c930d63d/

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/binutils/binutils.mk

@@ -8,8 +8,13 @@
 # If not, we do like other packages
 BINUTILS_VERSION = $(call qstrip,$(BR2_BINUTILS_VERSION))
 ifeq ($(BINUTILS_VERSION),)
+ifeq ($(BR2_avr32),y)
+# avr32 uses a special version
+BINUTILS_VERSION = 2.18-avr32-1.0.1
+else
 BINUTILS_VERSION = 2.21
 endif
+endif
 
 BINUTILS_SOURCE = binutils-$(BINUTILS_VERSION).tar.bz2
 BINUTILS_SITE = $(BR2_GNU_MIRROR)/binutils