Update to modern, maintained version of Arduino cmake toolchain

Source git repo:
https://github.com/a9183756-gh/Arduino-CMake-Toolchain

Works on Fedora 32.

Author: thomasjfox

cmake/Arduino-toolchain.cmake

@@ -0,0 +1,98 @@
+# Copyright (c) 2020 Arduino CMake Toolchain
+
+#=============================================================================
+# A toolchain for the Arduino compatile boards.
+# Please refer to README.md for the usage.
+
+# If the version of CMake used is below 3.7.0, exit with error.
+#
+# Intended to support CMake version 3.0.0, but there are limitations which
+# requires a minimum CMake version of 3.7.0. However, wherever possible, the
+# toolchain remains compatible with 3.0.0, looking for some workarounds for
+# the limitations in the future. The limitations are captured below.
+#
+# Version below 3.2.0 has no support for continue() command. Can be fixed.
+#
+# Version below 3.4.0 has no support for target properties BINARY_DIR,
+# SOURCE_DIR etc. These are required in target command generator expressions.
+#
+# Version below 3.6.0 has issues in identifying try_compile output for 
+# static library. So there are some errors during the configuration, but
+# may still possibly work.
+#
+# Version below 3.7.0 has no support for CMAKE_SYSTEM_CUSTOM_CODE, which
+# is required when there is some dynamic information, like Board options,
+# that needs to be included in the toolchain. Here just including the user
+# provided path will not work, because the user variables, cache or root
+# binary directory path etc. are not passed to try_compile.
+
+if (CMAKE_VERSION VERSION_LESS 3.7.0)
+	message(FATAL_ERROR "CMake version below 3.7.0 unsupported!!!")
+endif()
+
+# Save the policy state. We will restore it at the end.
+cmake_policy(PUSH)
+
+# Set policy to above 3.0.0
+cmake_policy(VERSION 3.0.0)
+
+# Interpret if() arguments without quotes as variables/keywords
+if (NOT CMAKE_VERSION VERSION_LESS 3.1)
+	cmake_policy(SET CMP0054 NEW)
+endif()
+
+#*****************************************************************************
+# Set system name and basic information
+set(CMAKE_SYSTEM_NAME "Arduino")
+
+# Set module path to enable local modules search
+set(ARDUINO_TOOLCHAIN_DIR "${CMAKE_CURRENT_LIST_DIR}")
+set(_ARDUINO_TOOLCHAIN_PARENT "${CMAKE_PARENT_LIST_FILE}")
+set(CMAKE_MODULE_PATH "${CMAKE_MODULE_PATH}" "${CMAKE_CURRENT_LIST_DIR}")
+set (ARDUINO_TOOLCHAIN_VERSION "1.0")
+
+# Include modules
+include(Arduino/System/BoardsIndex)
+include(Arduino/System/BoardToolchain)
+include(Arduino/System/BoardBuildTargets)
+
+#*****************************************************************************
+# For improved speed, indexing of boards is done only once during a 
+# cmake invocation. However, this toolchain file is included multiple
+# times in multiple contexts (system determination context, separate
+# context for each try compile etc.). After indexing, the selected
+# board's toolchain info is configured to a generated file that gets
+# included in every other inclusion of this toolchain.
+if (NOT _BOARD_INDEXING_COMPLETED)
+	get_property(_in_try_compile GLOBAL PROPERTY IN_TRY_COMPILE)
+	# IN_TRY_COMPILE check seems to be not enough. Check for parent
+	# script works, but may be undocumented!
+	get_filename_component(parent_script "${_ARDUINO_TOOLCHAIN_PARENT}"
+		NAME_WE)
+	if (parent_script STREQUAL "CMakeSystem")
+		check_board_options_changed(_b_changed)
+		if (NOT _b_changed)
+			set(_BOARD_INDEXING_COMPLETED TRUE)
+		endif()
+	endif()
+endif()
+
+if (NOT _BOARD_INDEXING_COMPLETED)
+	SetupBoardToolchain()
+	set(CMAKE_SYSTEM_CUSTOM_CODE
+		"include(\"${CMAKE_BINARY_DIR}/ArduinoSystem.cmake\")"
+	)
+	set (_BOARD_INDEXING_COMPLETED TRUE)
+endif()
+
+# Search for programs in the build host directories
+set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM BOTH)
+# For libraries and headers in the target directories
+set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
+set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
+
+# Do not try to link during the configure time, due to the dependency on the
+# core, which we do not have a target yet.
+set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
+
+cmake_policy(POP)