acceppt .keep file in src/<target_type>/ directories

CMakeLists.txt

@@ -48,8 +48,8 @@ FOREACH(target_type_dir ${target_types})
     GET_FILENAME_COMPONENT(target_type ${target_type_dir} NAME)
     FILE(GLOB target_directories "${target_type_dir}/*/")
     FOREACH(target_directory ${target_directories})
+      GET_FILENAME_COMPONENT(target_name ${target_directory} NAME)
       IF(IS_DIRECTORY ${target_directory})
-        GET_FILENAME_COMPONENT(target_name ${target_directory} NAME)
         MESSAGE("Creating build instructions for ${target_name}")
         FILE(GLOB target_sources "${target_directory}/*.cpp" "${target_directory}/*.c")
         FILE(GLOB target_headers "${target_directory}/include/*.*")
@@ -65,7 +65,11 @@ FOREACH(target_type_dir ${target_types})
         TARGET_INCLUDE_DIRECTORIES(${target_name} PRIVATE ${target_directory}/include)
         ADD_DEPS(${target_directory})
       ELSE()
-        MESSAGE(FATAL_ERROR "${target_directory} is no directory")
+        STRING(COMPARE EQUAL ${target_name} .keep is_keep)
+        IF(${is_keep})
+        ELSE()
+          MESSAGE(FATAL_ERROR "${target_directory} is no directory")
+        ENDIF()
       ENDIF()
     ENDFOREACH()
   ELSE()
@@ -105,7 +109,7 @@ FOREACH(test_type_dir ${test_types})
           MESSAGE(FATAL_ERROR "Error: unknown test type ${test_type}")
         ENDIF()
       ELSE()
-        string(COMPARE EQUAL ${test_target} .keep is_keep)
+        STRING(COMPARE EQUAL ${test_target} .keep is_keep)
         IF(${is_keep})
         ELSE()
           MESSAGE(FATAL_ERROR "${test_target_dir} is no directory")