Fix building host valgrind for TARGET_ARCH=x86

The entire valgrind build was disabled when TARGET_ARCH=x86.  It
should still build the host valgrind tool even if the target arch
is not supported.  Use LOCAL_MODULE_TARGET_ARCH instead of a
conditional.

Test: lunch aosp_x86-eng && m checkbuild
Change-Id: I89de9f9675d30ea3a760339798ed41bc3eaa72c3
diff --git a/Android.build_one.mk b/Android.build_one.mk
index 62d2c47..126ad1c 100644
--- a/Android.build_one.mk
+++ b/Android.build_one.mk
@@ -14,6 +14,8 @@
 
 include $(CLEAR_VARS)
 
+LOCAL_MODULE_TARGET_ARCH := $(VALGRIND_SUPPORTED_ARCH)
+
 LOCAL_ARM_MODE := arm
 ifeq ($(vg_build_second_arch),true)
 LOCAL_MULTILIB := 32