build speedup: Do not use shell 'find' function to look for NOTICE files.

The GNU Make wildcard function can be used to look for a specific file and
is _much_ faster than invoking the find command through $(shell ...).

Since notice_files.mk is included by base_rules.mk for each and every module
in the build tree, this represents a considerable speed-up. For example, when
building the full-eng product from the AOSP tree, the no-op "make" goes from
21 seconds to 16 seconds with this patch applied.

Change-Id: Ideb1bb74d5bfbb650834fa4b6e151ff24dcd0150
diff --git a/core/notice_files.mk b/core/notice_files.mk
index fd76d51..74beb49 100644
--- a/core/notice_files.mk
+++ b/core/notice_files.mk
@@ -2,9 +2,9 @@
 ## Track NOTICE files
 ###########################################################
 
-notice_file:=$(shell find $(LOCAL_PATH) -maxdepth 1 -name NOTICE)
+notice_file:=$(strip $(wildcard $(LOCAL_PATH)/NOTICE))
 
-ifneq ($(strip $(notice_file)),)
+ifdef notice_file
 
 # This relies on the name of the directory in PRODUCT_OUT matching where
 # it's installed on the target - i.e. system, data, etc.  This does