cmake: Add TristateOption module

cmake/module/TristateOption.cmake

@@ -0,0 +1,21 @@
+# Copyright (c) 2023 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+# A tri-state option with three possible values: AUTO, OFF and ON (case-insensitive).
+# TODO: This function will be removed before merging into master.
+function(tristate_option variable description_text auto_means_on_condition_text default_value)
+  set(${variable} ${default_value} CACHE STRING
+    "${description_text} \"AUTO\" means \"ON\" ${auto_means_on_condition_text}"
+  )
+
+  set(expected_values AUTO OFF ON)
+  set_property(CACHE ${variable} PROPERTY STRINGS ${expected_values})
+
+  string(TOUPPER "${${variable}}" value)
+  if(NOT value IN_LIST expected_values)
+    message(FATAL_ERROR "${variable} value is \"${${variable}}\", but must be one of \"AUTO\", \"OFF\" or \"ON\".")
+  endif()
+
+  set(${${variable}} ${value} PARENT_SCOPE)
+endfunction()