cmake: add comments to feature check options applied globally

Add comments saying when we want values set in feature check option
variables to apply to all feature checks, globally. These are currently:
`ws2_32` and `socket` libraries, and `-D_WIN32_WINNT=` macro.

Also use `list(APPEND ...)` for the libraries to avoid overwriting
potentially existing values.

Cherry-picked from #15157
Closes #15253

diff --git a/CMake/Macros.cmake b/CMake/Macros.cmake
index 3ed0a4982560028f06712693989d319d91e2fd88..62e0898df714ff24054847719e8e1d5fcacd690e 100644 (file)
--- a/CMake/Macros.cmake
+++ b/CMake/Macros.cmake
@@ -31,7 +31,7 @@ macro(check_include_file_concat _file _variable)
   check_include_files("${CURL_INCLUDES};${_file}" ${_variable})
   if(${_variable})
     set(CURL_INCLUDES ${CURL_INCLUDES} ${_file})
-    set(CURL_TEST_DEFINES "${CURL_TEST_DEFINES} -D${_variable}")
+    set(CURL_TEST_DEFINES "${CURL_TEST_DEFINES} -D${_variable}")  # Apply to curl_internal_test()
   endif()
 endmacro()
 

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3594be790a2dcd8563479a54bb0a43944d2c59dd..29f17fb659da84cb43d94de9c422da139af991eb 100644 (file)
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -168,8 +168,8 @@ if(WIN32)
   set(CURL_TARGET_WINDOWS_VERSION "" CACHE STRING "Minimum target Windows version as hex string")
   if(CURL_TARGET_WINDOWS_VERSION)
     add_definitions("-D_WIN32_WINNT=${CURL_TARGET_WINDOWS_VERSION}")
-    list(APPEND CMAKE_REQUIRED_DEFINITIONS "-D_WIN32_WINNT=${CURL_TARGET_WINDOWS_VERSION}")
-    set(CURL_TEST_DEFINES "${CURL_TEST_DEFINES} -D_WIN32_WINNT=${CURL_TARGET_WINDOWS_VERSION}")
+    list(APPEND CMAKE_REQUIRED_DEFINITIONS "-D_WIN32_WINNT=${CURL_TARGET_WINDOWS_VERSION}")  # Apply to all feature checks
+    set(CURL_TEST_DEFINES "${CURL_TEST_DEFINES} -D_WIN32_WINNT=${CURL_TARGET_WINDOWS_VERSION}")  # Apply to curl_internal_test()
   endif()
 
   # Detect actual value of _WIN32_WINNT and store as HAVE_WIN32_WINNT
@@ -1490,9 +1490,9 @@ endif()
 
 # Check for some functions that are used
 if(WIN32)
-  set(CMAKE_REQUIRED_LIBRARIES "ws2_32")
+  list(APPEND CMAKE_REQUIRED_LIBRARIES "ws2_32")  # Apply to all feature checks
 elseif(HAVE_LIBSOCKET)
-  set(CMAKE_REQUIRED_LIBRARIES "socket")
+  list(APPEND CMAKE_REQUIRED_LIBRARIES "socket")  # Apply to all feature checks
 endif()
 
 check_symbol_exists("fnmatch"         "${CURL_INCLUDES};fnmatch.h" HAVE_FNMATCH)