Include the linenoise.h header in a cleaner way.

(This was a comment to an earlier change that I
overlooked.)
diff --git a/sh/Android.mk b/sh/Android.mk
index 958c3dc..b5e5c38 100644
--- a/sh/Android.mk
+++ b/sh/Android.mk
@@ -35,6 +35,8 @@
 
 LOCAL_STATIC_LIBRARIES := liblinenoise
 
+LOCAL_C_INCLUDES += system/core/liblinenoise
+
 make_ash_files: PRIVATE_SRC_FILES := $(SRC_FILES)
 make_ash_files: PRIVATE_CFLAGS := $(LOCAL_CFLAGS)
 make_ash_files: