Support .asm being compiled by yasm targeted for x86_64.

Change-Id: Ia6425c38dd2f7ad2dc697213cd61b7515b9e7aff
diff --git a/core/definitions.mk b/core/definitions.mk
index 4bc51d3..fb91e13 100644
--- a/core/definitions.mk
+++ b/core/definitions.mk
@@ -1051,7 +1051,7 @@
 @mkdir -p $(dir $@)
 $(hide) $(YASM) \
     $(addprefix -I , $(PRIVATE_C_INCLUDES)) \
-    -f elf32 -m x86 \
+    $($(PRIVATE_2ND_ARCH_VAR_PREFIX)TARGET_GLOBAL_YASM_FLAGS) \
     $(PRIVATE_ASFLAGS) \
     -o $@ $<
 endef