Enables x86-atom as a valid TARGET_ARCH_VARIANT for the simulator build.

Change-Id: Idbceb6c7d4117fbecd35e4261330e6405666189e
diff --git a/core/combo/TARGET_linux-x86.mk b/core/combo/TARGET_linux-x86.mk
index 1477ae6..b3dd1d6 100644
--- a/core/combo/TARGET_linux-x86.mk
+++ b/core/combo/TARGET_linux-x86.mk
@@ -25,7 +25,9 @@
 TARGET_GLOBAL_CFLAGS := $(HOST_GLOBAL_CFLAGS) -m32
 TARGET_GLOBAL_LDFLAGS := $(HOST_GLOBAL_LDFLAGS) -m32 -lpthread
 TARGET_NO_UNDEFINED_LDFLAGS := $(HOST_NO_UNDEFINED_LDFLAGS)
+ifeq ($(strip $(TARGET_ARCH_VARIANT)),)
 TARGET_ARCH_VARIANT := x86
+endif
 else #simulator
 
 # Provide a default variant.