export cmake option when developer use CMake FetchContent (#591)

For example, use the following cmake config
```
include(FetchContent)
FetchContent_Declare(
        yalantinglibs
        GIT_REPOSITORY https://github.com/alibaba/yalantinglibs.git
        GIT_TAG xxx # use the least commit id
        GIT_SHALLOW 1 # optional ( --depth=1 )
)
FetchContent_MakeAvailable(yalantinglibs)
add_executable(demo main.cpp)
target_link_libraries(demo PRIVATE yalantinglibs)
```

you can use `cmake -DENABLE_STRUCT_PACK_UNPORTABLE_TYPE=ON ..`,
the option `ENABLE_STRUCT_PACK_UNPORTABLE_TYPE=ON` will be used when building yalantinglibs

CMakeLists.txt

@@ -28,5 +28,8 @@ if(CMAKE_PROJECT_NAME STREQUAL "yaLanTingLibs") # if ylt is top-level project
         include(cmake/config.cmake)
         # add project's source such as unit test, example & benchmark
         include(cmake/subdir.cmake)
+else ()
+        # add project config, such as enable_ssl.
+        include(cmake/config.cmake)
 endif()
 

cmake/config.cmake

@@ -3,43 +3,70 @@ option(ENABLE_SSL "Enable ssl support" OFF)
 message(STATUS "ENABLE_SSL: ${ENABLE_SSL}")
 if (ENABLE_SSL)
     find_package(OpenSSL REQUIRED)
-    add_compile_definitions(YLT_ENABLE_SSL)
-    link_libraries(OpenSSL::SSL OpenSSL::Crypto)
+    if(CMAKE_PROJECT_NAME STREQUAL "yaLanTingLibs")
+        add_compile_definitions(YLT_ENABLE_SSL)
+        link_libraries(OpenSSL::SSL OpenSSL::Crypto)
+    else ()
+        target_compile_definitions(yalantinglibs INTERFACE YLT_ENABLE_SSL)
+        target_link_libraries(yalantinglibs INTERFACE OpenSSL::SSL OpenSSL::Crypto)
+    endif ()
 endif ()
 
 option(ENABLE_PMR "Enable pmr support" OFF)
 message(STATUS "ENABLE_PMR: ${ENABLE_PMR}")
 if (ENABLE_PMR)
-    add_compile_definitions(YLT_ENABLE_PMR IGUANA_ENABLE_PMR)
+    if(CMAKE_PROJECT_NAME STREQUAL "yaLanTingLibs")
+        add_compile_definitions(YLT_ENABLE_PMR IGUANA_ENABLE_PMR)
+    else ()
+        target_compile_definitions(yalantinglibs INTERFACE YLT_ENABLE_PMR IGUANA_ENABLE_PMR)
+    endif ()
 endif ()
 
 option(ENABLE_IO_URING "Enable io_uring" OFF)
 message(STATUS "ENABLE_IO_URING: ${ENABLE_IO_URING}")
 if (ENABLE_IO_URING)
   find_package(uring REQUIRED)
   message(STATUS "Use IO_URING for all I/O in linux")
-  add_compile_definitions(ASIO_HAS_IO_URING ASIO_DISABLE_EPOLL ASIO_HAS_FILE YLT_ENABLE_FILE_IO_URING)
-  link_libraries(uring)
+  if(CMAKE_PROJECT_NAME STREQUAL "yaLanTingLibs")
+      add_compile_definitions(ASIO_HAS_IO_URING ASIO_DISABLE_EPOLL ASIO_HAS_FILE YLT_ENABLE_FILE_IO_URING)
+      link_libraries(uring)
+  else ()
+      target_compile_definitions(yalantinglibs INTERFACE ASIO_HAS_IO_URING ASIO_DISABLE_EPOLL ASIO_HAS_FILE YLT_ENABLE_FILE_IO_URING)
+      target_link_libraries(yalantinglibs INTERFACE uring)
+  endif ()
 endif()
 
 option(ENABLE_FILE_IO_URING "Enable file io_uring" OFF)
 if (NOT ENABLE_IO_URING)
   if(ENABLE_FILE_IO_URING)
     find_package(uring REQUIRED)
     message(STATUS "Enable io_uring for file I/O in linux")
-    add_compile_definitions(ASIO_HAS_IO_URING ASIO_HAS_FILE YLT_ENABLE_FILE_IO_URING)
-    link_libraries(uring)
+    if(CMAKE_PROJECT_NAME STREQUAL "yaLanTingLibs")
+        add_compile_definitions(ASIO_HAS_IO_URING ASIO_HAS_FILE YLT_ENABLE_FILE_IO_URING)
+        link_libraries(uring)
+    else ()
+        target_compile_definitions(yalantinglibs INTERFACE ASIO_HAS_IO_URING ASIO_HAS_FILE YLT_ENABLE_FILE_IO_URING)
+        target_link_libraries(yalantinglibs INTERFACE uring)
+    endif ()
   endif()
 endif()
 
 option(ENABLE_STRUCT_PACK_UNPORTABLE_TYPE "enable struct_pack unportable type(like wchar_t)" OFF)
 message(STATUS "ENABLE_STRUCT_PACK_UNPORTABLE_TYPE: ${ENABLE_STRUCT_PACK_UNPORTABLE_TYPE}")
 if(ENABLE_STRUCT_PACK_UNPORTABLE_TYPE)
-  add_compile_definitions(STRUCT_PACK_ENABLE_UNPORTABLE_TYPE)
+    if(CMAKE_PROJECT_NAME STREQUAL "yaLanTingLibs")
+        add_compile_definitions(STRUCT_PACK_ENABLE_UNPORTABLE_TYPE)
+    else ()
+        target_compile_definitions(yalantinglibs INTERFACE STRUCT_PACK_ENABLE_UNPORTABLE_TYPE)
+    endif ()
 endif()
 
 option(ENABLE_STRUCT_PACK_OPTIMIZE "enable struct_pack optimize(but cost more compile time)" OFF)
 message(STATUS "ENABLE_STRUCT_PACK_OPTIMIZE: ${ENABLE_STRUCT_PACK_OPTIMIZE}")
 if(ENABLE_STRUCT_PACK_OPTIMIZE)
-  add_compile_definitions(ENABLE_STRUCT_PACK_OPTIMIZE)
+    if(CMAKE_PROJECT_NAME STREQUAL "yaLanTingLibs")
+        add_compile_definitions(ENABLE_STRUCT_PACK_OPTIMIZE)
+    else ()
+        target_compile_definitions(yalantinglibs INTERFACE ENABLE_STRUCT_PACK_OPTIMIZE)
+    endif ()
 endif()