cmake: skip superfluous hex2dec conversion using math expr

CMake seems to be able to compare two hex values just fine.
Also make sure CURL_TARGET_WINDOWS_VERSION is respected.

Assisted-by: Marcel Raad
Reviewed-by: Viktor Szakats
Reported-by: Keitagit-kun on github

Follow up to #9312
Fixes #9406
Closes #9411

CMakeLists.txt

@@ -87,6 +87,7 @@ if(WIN32)
   if(CURL_TARGET_WINDOWS_VERSION)
     add_definitions(-D_WIN32_WINNT=${CURL_TARGET_WINDOWS_VERSION})
     set(CMAKE_REQUIRED_DEFINITIONS "${CMAKE_REQUIRED_DEFINITIONS} -D_WIN32_WINNT=${CURL_TARGET_WINDOWS_VERSION}")
+    set(CURL_TEST_DEFINES "${CURL_TEST_DEFINES} -D_WIN32_WINNT=${CURL_TARGET_WINDOWS_VERSION}")
   endif()
   if(ENABLE_UNICODE)
     add_definitions(-DUNICODE -D_UNICODE)
@@ -1166,9 +1167,8 @@ if(WIN32)
   curl_internal_test(HAVE_WIN32_WINNT)
   if(HAVE_WIN32_WINNT)
     string(REGEX MATCH ".*_WIN32_WINNT=0x[0-9a-fA-F]+" OUTPUT "${OUTPUT}")
-    string(REGEX REPLACE ".*_WIN32_WINNT=" "" OUTPUT "${OUTPUT}")
-    math(EXPR HAVE_WIN32_WINNT "${OUTPUT}" OUTPUT_FORMAT DECIMAL)
-    message(STATUS "Found _WIN32_WINNT=${OUTPUT} (${HAVE_WIN32_WINNT})")
+    string(REGEX REPLACE ".*_WIN32_WINNT=" "" HAVE_WIN32_WINNT "${OUTPUT}")
+    message(STATUS "Found _WIN32_WINNT=${HAVE_WIN32_WINNT}")
   endif()
   # avoid storing HAVE_WIN32_WINNT in CMake cache
   unset(HAVE_WIN32_WINNT CACHE)