cmake: Enable win32 threaded resolver by default

- Turn on USE_THREADS_WIN32 in Windows if ares isn't on

This change is similar to what we already do in the autotools build.

CMakeLists.txt

@@ -42,6 +42,7 @@ cmake_minimum_required(VERSION 2.8 FATAL_ERROR)
 set(CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/CMake;${CMAKE_MODULE_PATH}")
 include(Utilities)
 include(Macros)
+include(CMakeDependentOption)
 
 project( CURL C )
 
@@ -74,8 +75,14 @@ include_directories( ${CURL_SOURCE_DIR}/include )
 option(BUILD_CURL_EXE "Set to ON to build cURL executable." ON)
 option(CURL_STATICLIB "Set to ON to build libcurl with static linking." OFF)
 option(ENABLE_ARES "Set to ON to enable c-ares support" OFF)
-option(ENABLE_THREADED_RESOLVER "Set to ON to enable POSIX threaded DNS lookup" OFF)
-
+if(WIN32)
+  CMAKE_DEPENDENT_OPTION(ENABLE_THREADED_RESOLVER
+                         "Set to ON to enable threaded DNS lookup"
+                         ON "NOT ENABLE_ARES"
+                         OFF)
+else()
+  option(ENABLE_THREADED_RESOLVER "Set to ON to enable POSIX threaded DNS lookup" OFF)
+endif()
 option(ENABLE_DEBUG "Set to ON to enable curl debug features" OFF)
 option(ENABLE_CURLDEBUG "Set to ON to build with TrackMemory feature enabled" OFF)
 
@@ -250,13 +257,17 @@ if(WIN32)
 endif(WIN32)
 
 if(ENABLE_THREADED_RESOLVER)
-  check_include_file_concat("pthread.h" HAVE_PTHREAD_H)
-  if(HAVE_PTHREAD_H)
-    set(CMAKE_THREAD_PREFER_PTHREAD 1)
-    find_package(Threads)
-    if(CMAKE_USE_PTHREADS_INIT)
-      set(CURL_LIBS ${CURL_LIBS} ${CMAKE_THREAD_LIBS_INIT})
-      set(USE_THREADS_POSIX 1)
+  if(WIN32)
+    set(USE_THREADS_WIN32 ON)
+  else()
+    check_include_file_concat("pthread.h" HAVE_PTHREAD_H)
+    if(HAVE_PTHREAD_H)
+      set(CMAKE_THREAD_PREFER_PTHREAD 1)
+      find_package(Threads)
+      if(CMAKE_USE_PTHREADS_INIT)
+        set(CURL_LIBS ${CURL_LIBS} ${CMAKE_THREAD_LIBS_INIT})
+        set(USE_THREADS_POSIX 1)
+      endif()
     endif()
   endif()
 endif()
@@ -1062,7 +1073,7 @@ _add_if("OpenSSL"       SSL_ENABLED AND USE_OPENSSL)
 _add_if("IPv6"          ENABLE_IPV6)
 _add_if("unix-sockets"  USE_UNIX_SOCKETS)
 _add_if("libz"          HAVE_LIBZ)
-_add_if("AsynchDNS"     USE_ARES OR USE_THREADS_POSIX)
+_add_if("AsynchDNS"     USE_ARES OR USE_THREADS_POSIX OR USE_THREADS_WIN32)
 _add_if("IDN"           HAVE_LIBIDN)
 _add_if("Largefile"     (CURL_SIZEOF_CURL_OFF_T GREATER 4) AND
                         ((SIZEOF_OFF_T GREATER 4) OR USE_WIN32_LARGE_FILES))

lib/curl_config.h.cmake

@@ -906,6 +906,9 @@
 /* Define if you want to enable POSIX threaded DNS lookup */
 #cmakedefine USE_THREADS_POSIX 1
 
+/* Define if you want to enable WIN32 threaded DNS lookup */
+#cmakedefine USE_THREADS_WIN32 1
+
 /* Define to disable non-blocking sockets. */
 #cmakedefine USE_BLOCKING_SOCKETS 1