Make sure that CURL_TARGET_WINDOWS_VERSION is always defined

Author: negrutiu

_Build.bat

@@ -683,6 +683,12 @@ set CMAKE_CURL_VARIABLES=!CMAKE_CURL_VARIABLES! ^
 
 if /i "%CONFIG%" equ "Debug" set CMAKE_CURL_VARIABLES=!CMAKE_CURL_VARIABLES! -DENABLE_CURLDEBUG=ON -DENABLE_DEBUG=ON -DCMAKE_DEBUG_POSTFIX:STRING=""
 
+REM | CURL requires valid CURL_TARGET_WINDOWS_VERSION
+REM | https://github.com/curl/curl/issues/9406
+for /f "usebackq delims=*" %%s in (`powershell -ExecutionPolicy bypass -Command "if ('!BUILD_C_FLAGS!' -match '-D_WIN32_WINNT=(?<hexver>0x[0-9a-fA-F]+)') { $Matches.hexver }"`) do set CURL_TARGET_WINDOWS_VERSION=%%s
+if "%CURL_TARGET_WINDOWS_VERSION%" equ "" set CURL_TARGET_WINDOWS_VERSION=0x0601
+set CMAKE_CURL_VARIABLES=!CMAKE_CURL_VARIABLES! -DCURL_TARGET_WINDOWS_VERSION=%CURL_TARGET_WINDOWS_VERSION%
+
 REM | curl(static CRT)
 if /i "%BUILDER%" equ "MSVC" (
 	if /i "%CRT%" equ "static" set CMAKE_CURL_VARIABLES=!CMAKE_CURL_VARIABLES! -DCURL_STATIC_CRT=ON