Friendlier message for ABI reference update

This change is to let people to just copy & paste the update command

Test: break the ABI of libbinder intentionally and make.
The message includes absolute path to the create_reference_dump.py tool.

Change-Id: If7703d64be1f51ea4b054aa1e815276e1d6dbc14
diff --git a/cc/builder.go b/cc/builder.go
index cec0056..cb09d09 100644
--- a/cc/builder.go
+++ b/cc/builder.go
@@ -203,7 +203,7 @@
 
 			commandStr := "($sAbiDiffer $allowFlags -lib $libName -arch $arch -check-all-apis -o ${out} -new $in -old $referenceDump)"
 			distAbiDiffDir := android.PathForDist(ctx, "abidiffs")
-			commandStr += "|| (echo ' ---- Please update abi references by running platform/development/vndk/tools/header-checker/utils/create_reference_dumps.py -l ${libName} ----'"
+			commandStr += "|| (echo ' ---- Please update abi references by running $$ANDROID_BUILD_TOP/development/vndk/tools/header-checker/utils/create_reference_dumps.py -l ${libName} ----'"
 			if distAbiDiffDir.Valid() {
 				commandStr += " && (mkdir -p " + distAbiDiffDir.String() + " && cp ${out} " + distAbiDiffDir.String() + ")"
 			}