[UGLY HACK] replace older compiler with the new one if it exists

To overcome https://github.com/arduino/Arduino/issues/5168, find a better way please :)

Author: facchinm

src/arduino.cc/builder/add_missing_build_properties_from_parent_platform_txt_files.go

@@ -30,6 +30,7 @@
 package builder
 
 import (
+	"arduino.cc/builder/constants"
 	"arduino.cc/builder/types"
 	"arduino.cc/json_package_index"
 )
@@ -68,6 +69,13 @@ func (s *OverridePropertiesWithJsonInfo) Run(ctx *types.Context) error {
 
 		buildProperties.Merge(newBuildProperties)
 
+		// HACK!!! To overcome AVR core 1.6.12 lto problems, replace avr-gcc-4.8.1-arduino5 with
+		// 4.9.2-atmel3.5.3-arduino2 if it exists
+		if buildProperties[constants.HACK_PROPERTIES_AVR_GCC_NEW] != "" {
+			buildProperties[constants.HACK_PROPERTIES_AVR_GCC_OLD] =
+				"{" + constants.HACK_PROPERTIES_AVR_GCC_NEW + "}"
+		}
+
 		ctx.BuildProperties = buildProperties
 	}
 

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

@@ -210,3 +210,5 @@ const SKETCH_FOLDER_SRC = "src"
 const TOOL_NAME = "name"
 const TOOL_URL = "url"
 const TOOL_VERSION = "version"
+const HACK_PROPERTIES_AVR_GCC_NEW = BUILD_PROPERTIES_RUNTIME_TOOLS_PREFIX + "avr-gcc-arduino-4.9.2-atmel3.5.3-arduino2" + BUILD_PROPERTIES_RUNTIME_TOOLS_SUFFIX
+const HACK_PROPERTIES_AVR_GCC_OLD = BUILD_PROPERTIES_RUNTIME_TOOLS_PREFIX + "avr-gcc-arduino-4.8.1-arduino5" + BUILD_PROPERTIES_RUNTIME_TOOLS_SUFFIX