tools/Android.mk: add any extra program sources

v2: remove unintended change and fix source file duplication errors
    (Derek Morton)

Cc: Derek Morton <derek.j.morton@intel.com>
Signed-off-by: Thomas Wood <thomas.wood@intel.com>
diff --git a/tools/Android.mk b/tools/Android.mk
index 39f4512..fbba579 100644
--- a/tools/Android.mk
+++ b/tools/Android.mk
@@ -7,7 +7,11 @@
 define add_tool
     include $(CLEAR_VARS)
 
-    LOCAL_SRC_FILES := $1.c
+    ifeq ($($(1)_SOURCES),)
+        LOCAL_SRC_FILES := $1.c
+    else
+        LOCAL_SRC_FILES := $($(1)_SOURCES)
+    endif
 
     LOCAL_CFLAGS += -DHAVE_TERMIOS_H
     LOCAL_CFLAGS += -DHAVE_STRUCT_SYSINFO_TOTALRAM