Show filename in "using precompiled core" message

This is more consistent with other similar messages (e.g. "Using
previously compiled file") and provides a direct hint to the user where
this cached core can be deleted if needed.

Signed-off-by: Matthijs Kooijman <matthijs@stdin.nl>

Author: matthijskooijman

src/arduino.cc/builder/phases/core_builder.go

@@ -108,7 +108,7 @@ func compileCore(buildPath string, buildCachePath string, buildProperties proper
 		if canUseArchivedCore {
 			// use archived core
 			if verbose {
-				logger.Println(constants.LOG_LEVEL_INFO, "Using precompiled core")
+				logger.Println(constants.LOG_LEVEL_INFO, "Using precompiled core: {0}", targetArchivedCore)
 			}
 			return targetArchivedCore, variantObjectFiles, nil
 		}