Depend on .git/COMMIT_EDITMSG instead of .git/*

Change-Id: I95a4634c55a5350b740acf70b9d997ccd2a9b8f2
diff --git a/libbcc-gen-build-stamp.mk b/libbcc-gen-build-stamp.mk
index 6aa4475..1c8a685 100644
--- a/libbcc-gen-build-stamp.mk
+++ b/libbcc-gen-build-stamp.mk
@@ -50,7 +50,7 @@
 $(GEN): PRIVATE_CUSTOM_TOOL = $(PRIVATE_PATH)/tools/gen-build-stamp.py \
                               $(PRIVATE_PATH) $(PRIVATE_DEPS) > $@
 $(GEN): $(LOCAL_PATH)/tools/gen-build-stamp.py $(LOCAL_LIBBCC_LIB_DEPS) \
-        $(wildcard $(LOCAL_PATH)/.git/*)
+        $(wildcard $(LOCAL_PATH)/.git/COMMIT_EDITMSG)
 	$(transform-generated-source)
 
 LOCAL_GENERATED_SOURCES += $(GEN)