cmake: fix VERSION file path

cmake fails when the variable CMAKE_SOURCE_DIR does not point to
the libmetal directory.
This is the case, for example, for the Zephyr project.

Fix by defining LIBMETAL_ROOT_DIR in the main CmakeLists.txt.

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>

CMakeLists.txt

@@ -7,6 +7,8 @@ if (POLICY CMP0077)
   cmake_policy(SET CMP0077 NEW)
 endif()
 
+set (LIBMETAL_ROOT_DIR "${CMAKE_CURRENT_SOURCE_DIR}")
+
 list (APPEND CMAKE_MODULE_PATH
       "${CMAKE_CURRENT_SOURCE_DIR}/cmake"
       "${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules"

cmake/options.cmake

@@ -1,4 +1,4 @@
-file(READ ${CMAKE_SOURCE_DIR}/VERSION ver)
+file(READ ${LIBMETAL_ROOT_DIR}/VERSION ver)
 
 string(REGEX MATCH "VERSION_MAJOR = ([0-9]*)" _ ${ver})
 set(PROJECT_VERSION_MAJOR ${CMAKE_MATCH_1})