cmake: Add CMake package registration script

This commit adds a universal CMake script that automates the
registration of the `Zephyr-sdk` CMake package in the user package
registry.

Signed-off-by: Stephanos Ioannidis <[email protected]>

Author: stephanosio

cmake/zephyr_sdk_export.cmake

@@ -0,0 +1,43 @@
+# SPDX-License-Identifier: Apache-2.0
+
+# The purpose of this CMake file is to register the Zephyr-sdk package in:
+#
+#   Linux/macOS: ~/.cmake/packages/Zephyr-sdk
+#       Windows: HKEY_CURRENT_USER
+#
+# By registering the Zephyr-sdk package, the Zephyr build system can locate the
+# required version of Zephyr SDK through `find_package(Zephyr-sdk)` even when
+# ZEPHYR_SDK_INSTALL_DIR is not explicitly set.
+#
+# Register the Zephyr-sdk package by running `cmake -P zephyr_sdk_export.cmake`
+# in this directory.
+
+set(MD5_INFILE "current_path.txt")
+
+# We write CMAKE_CURRENT_LIST_DIR into MD5_INFILE, as the content of that file
+# will be used for MD5 calculation.  This means we effectively get the MD5 of
+# CMAKE_CURRENT_LIST_DIR which must be used for CMake user package registry.
+file(WRITE ${CMAKE_CURRENT_LIST_DIR}/${MD5_INFILE} ${CMAKE_CURRENT_LIST_DIR})
+execute_process(COMMAND ${CMAKE_COMMAND} -E md5sum ${CMAKE_CURRENT_LIST_DIR}/${MD5_INFILE}
+                OUTPUT_VARIABLE MD5_SUM
+)
+string(SUBSTRING ${MD5_SUM} 0 32 MD5_SUM)
+if(WIN32)
+  execute_process(COMMAND ${CMAKE_COMMAND}
+                  -E write_regv
+                  "HKEY_CURRENT_USER\\Software\\Kitware\\CMake\\Packages\\Zephyr-sdk\;${MD5_SUM}"
+                  "${CMAKE_CURRENT_LIST_DIR}"
+  )
+else()
+  file(WRITE $ENV{HOME}/.cmake/packages/Zephyr-sdk/${MD5_SUM} ${CMAKE_CURRENT_LIST_DIR})
+endif()
+
+message("Zephyr-sdk (${CMAKE_CURRENT_LIST_DIR})")
+message("has been added to the user package registry in:")
+if(WIN32)
+  message("HKEY_CURRENT_USER\\Software\\Kitware\\CMake\\Packages\\Zephyr-sdk\n")
+else()
+  message("~/.cmake/packages/Zephyr-sdk\n")
+endif()
+
+file(REMOVE ${CMAKE_CURRENT_LIST_DIR}/${MD5_INFILE})