Only use builtin_tools_versions.txt if its folder is builtin

Otherwise, all board manager folder was considered builtin (due to the recursive search in findBuiltinToolsVersionsFile() )

Fixes #246

Author: facchinm

src/arduino.cc/builder/constants/constants.go

@@ -157,6 +157,7 @@ const MSG_BUILD_OPTIONS_CHANGED = "Build options changed, rebuilding all"
 const MSG_CANT_FIND_SKETCH_IN_PATH = "Unable to find {0} in {1}"
 const MSG_FQBN_INVALID = "{0} is not a valid fully qualified board name. Required format is targetPackageName:targetPlatformName:targetBoardName."
 const MSG_INVALID_QUOTING = "Invalid quoting: no closing [{0}] char found."
+const MSG_IGNORED_BUILTIN_TOOLS_TXT = "Skipping {0}; please consider removing that file since it may hurt older Arduino installations"
 const MSG_LIB_LEGACY = "(legacy)"
 const MSG_LIBRARIES_MULTIPLE_LIBS_FOUND_FOR = "Multiple libraries were found for \"{0}\""
 const MSG_LIBRARIES_NOT_USED = " Not used: {0}"

src/arduino.cc/builder/tools_loader.go

@@ -52,6 +52,13 @@ func (s *ToolsLoader) Run(ctx *types.Context) error {
 		if err != nil {
 			return i18n.WrapError(err)
 		}
+		builtinHardwareFolder, err := filepath.Abs(filepath.Join(ctx.BuiltInLibrariesFolders[0], ".."))
+
+		if builtinToolsVersionsFile != constants.EMPTY_STRING && !strings.Contains(builtinToolsVersionsFile, builtinHardwareFolder) {
+			ctx.GetLogger().Println(constants.LOG_LEVEL_WARN, constants.MSG_IGNORED_BUILTIN_TOOLS_TXT, builtinToolsVersionsFile)
+			builtinToolsVersionsFile = constants.EMPTY_STRING
+		}
+
 		if builtinToolsVersionsFile != constants.EMPTY_STRING {
 			err = loadToolsFrom(&tools, builtinToolsVersionsFile)
 			if err != nil {