app func & shader generation

CMakeLists.txt

/* ... */

#=== EXECUTABLE func
function(app app_name)
    if(APPLE)
        add_executable(${app_name} MACOSX_BUNDLE ${ARGN} )
    elseif(WIN32)
        add_executable(${app_name} WIN32 ${ARGN})
    else()
        add_executable(${app_name} ${ARGN})
    endif()
endfunction()

if (${CMAKE_HOST_SYSTEM_NAME} STREQUAL "Windows")
    set(TOOLS_DIR "${PROJECT_SOURCE_DIR}/tools/win32")    
elseif (${CMAKE_HOST_SYSTEM_NAME} STREQUAL "Darwin")
    set(TOOLS_DIR "${PROJECT_SOURCE_DIR}/tools/osx")
elseif(${CMAKE_HOST_SYSTEM_NAME} STREQUAL "Linux")
    set(TOOLS_DIR "${PROJECT_SOURCE_DIR}/tools/linux")
endif()

function(shd_shader target_name)
    message(STATUS "Found shd: ${SHD_BIN_PATH}")

    foreach(source_file ${ARGN})
        set (shd_output_file "${source_file}.h")
        add_custom_command(
            OUTPUT ${shd_output_file}
            COMMAND ${SHD_BIN_PATH}
            ARGS --input ${source_file} --slang ${slang} --output ${shd_output_file}
            DEPENDS ${source_file}
            WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
            COMMENT "Compiling ${slang}: ${shd_output_file}"
            VERBATIM
        )
        if(APPLE)
            target_sources(${target_name} PRIVATE ${shd_output_file})
        else()
            target_sources(${target_name} PRIVATE "${CMAKE_CURRENT_SOURCE_DIR}/${shd_output_file}" "${CMAKE_CURRENT_SOURCE_DIR}/${source_file}")
        endif()
    endforeach()
endfunction()

app(demo demo.c)
target_link_libraries(demo sokol)
shd_shader(demo shaders.glsl)