Define atrace_* functions for both target and host.

This change defines atrace_* functions for the host that act as
no-ops, which makes it easier to add tracing in ART.

Change-Id: I89397e83986686a2b6a6f245c25017eb379081b1
diff --git a/libcutils/Android.mk b/libcutils/Android.mk
index d890319..9f32307 100644
--- a/libcutils/Android.mk
+++ b/libcutils/Android.mk
@@ -59,7 +59,8 @@
         sockets.c \
 
     commonHostSources += \
-        ashmem-host.c
+        ashmem-host.c \
+        trace-host.c
 
 endif
 
@@ -116,7 +117,7 @@
         partition_utils.c \
         properties.c \
         qtaguid.c \
-        trace.c \
+        trace-dev.c \
         uevent.c \
 
 LOCAL_SRC_FILES_arm += \