Fix cross compilation (nm command)

Commit c261d774fb9093d00e0938a19f502fb220f62718 added one more binutils
tool: nm also needs a cross prefix.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1411070108-8954-1-git-send-email-sw@weilnetz.de
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
diff --git a/rules.mak b/rules.mak
index 1d73293..cf76b88 100644
--- a/rules.mak
+++ b/rules.mak
@@ -23,7 +23,7 @@
 QEMU_INCLUDES += -I$(<D) -I$(@D)
 
 WL_U := -Wl,-u,
-find-symbols = $(if $1, $(sort $(shell nm -P -g $1 | $2)))
+find-symbols = $(if $1, $(sort $(shell $(NM) -P -g $1 | $2)))
 defined-symbols = $(call find-symbols,$1,awk '$$2!="U"{print $$1}')
 undefined-symbols = $(call find-symbols,$1,awk '$$2=="U"{print $$1}')