Fix nasa#652, cmake-based OSAL config

Rather than CFE generating an osconfig.h file directly, it just
needs to select file(s) from the defs directory and pass them
to OSAL for the config.

cmake/arch_build.cmake

@@ -259,12 +259,18 @@ endfunction(cfs_app_do_install)
 #
 function(prepare)
 
-  # Generate the "osconfig.h" wrapper file as indicated by the configuration
-  # If specific system config options were not specified, use defaults
-  if (NOT OSAL_SYSTEM_OSCONFIG)
-    set(OSAL_SYSTEM_OSCONFIG default)
-  endif (NOT OSAL_SYSTEM_OSCONFIG)    
-  generate_config_includefile("inc/osconfig.h" osconfig.h ${OSAL_SYSTEM_OSCONFIG} ${TARGETSYSTEM})
+  # Choose the configuration file to use for OSAL on this system
+  set(OSAL_CONFIGURATION_FILE)
+  if (EXISTS "${MISSION_DEFS}/default_osconfig.cmake")
+    list(APPEND OSAL_CONFIGURATION_FILE "${MISSION_DEFS}/default_osconfig.cmake")
+  endif()
+  if (DEFINED OSAL_SYSTEM_OSCONFIG AND EXISTS "${MISSION_DEFS}/${OSAL_SYSTEM_OSCONFIG}_osconfig.cmake")
+    list(APPEND OSAL_CONFIGURATION_FILE "${MISSION_DEFS}/${OSAL_SYSTEM_OSCONFIG}_osconfig.cmake")
+  endif()
+  if (EXISTS "${MISSION_DEFS}/${TARGETSYSTEM}_osconfig.cmake")
+    list(APPEND OSAL_CONFIGURATION_FILE "${MISSION_DEFS}/${TARGETSYSTEM}_osconfig.cmake")
+  endif()
+  set(OSAL_CONFIGURATION_FILE ${OSAL_CONFIGURATION_FILE} PARENT_SCOPE)
 
   # Allow sources to "ifdef" certain things if running on simulated hardware
   # This should be used sparingly, typically to fake access to hardware that is not present