windows: simplify detecting and using system headers

- autotools, cmake: assume that if we detect Windows, `windows.h`,
  `winsock2.h` and `ws2tcpip.h` do exist.
- lib: fix 3 outlier `#if` conditions to use `USE_WINSOCK` instead of
  looking for `winsock2.h`.
- autotools: merge 3 Windows check methods into one.
- move Watt-32 and lwIP socket support to `setup-win32.h` from
  `config-win32.h`. It opens up using these with all build tools. Also
  merge logic with Windows Sockets.
- fix to assume Windows sockets with the mingw32ce toolchain.
  Follow-up to: 2748c64d60
- cmake: delete unused variable `signature_call_conv` since
  eb33ccd533.
- autotools: simplify `CURL_CHECK_WIN32_LARGEFILE` detection.
- examples/externalsocket: fix header order.
- cmake/OtherTests.cmake: delete Windows-specific `_source_epilogue`
  that wasn't used anymore.
- cmake/OtherTests.cmake: set `WIN32_LEAN_AND_MEAN` for test
  `SIZEOF_STRUCT_SOCKADDR_STORAGE`.

After this patch curl universally uses `_WIN32` to guard
Windows-specific logic. It guards Windows Sockets-specific logic with
`USE_WINSOCK` (this might need further work).

Reviewed-by: Jay Satiro
Closes #12495

CMake/CurlTests.c

@@ -164,13 +164,11 @@ int main(void) { ; return 0; }
 
 #ifdef HAVE_IOCTLSOCKET
 /* includes start */
-#ifdef HAVE_WINDOWS_H
+#ifdef _WIN32
 #  ifndef WIN32_LEAN_AND_MEAN
 #    define WIN32_LEAN_AND_MEAN
 #  endif
-#  ifdef HAVE_WINSOCK2_H
-#    include <winsock2.h>
-#  endif
+#  include <winsock2.h>
 #  include <windows.h>
 #endif
 int main(void)
@@ -186,13 +184,11 @@ int main(void)
 
 #ifdef HAVE_IOCTLSOCKET_CAMEL
 /* includes start */
-#ifdef HAVE_WINDOWS_H
+#ifdef _WIN32
 #  ifndef WIN32_LEAN_AND_MEAN
 #    define WIN32_LEAN_AND_MEAN
 #  endif
-#  ifdef HAVE_WINSOCK2_H
-#    include <winsock2.h>
-#  endif
+#  include <winsock2.h>
 #  include <windows.h>
 #endif
 int main(void)
@@ -207,13 +203,11 @@ int main(void)
 
 #ifdef HAVE_IOCTLSOCKET_CAMEL_FIONBIO
 /* includes start */
-#ifdef HAVE_WINDOWS_H
+#ifdef _WIN32
 #  ifndef WIN32_LEAN_AND_MEAN
 #    define WIN32_LEAN_AND_MEAN
 #  endif
-#  ifdef HAVE_WINSOCK2_H
-#    include <winsock2.h>
-#  endif
+#  include <winsock2.h>
 #  include <windows.h>
 #endif
 int main(void)
@@ -229,13 +223,11 @@ int main(void)
 
 #ifdef HAVE_IOCTLSOCKET_FIONBIO
 /* includes start */
-#ifdef HAVE_WINDOWS_H
+#ifdef _WIN32
 #  ifndef WIN32_LEAN_AND_MEAN
 #    define WIN32_LEAN_AND_MEAN
 #  endif
-#  ifdef HAVE_WINSOCK2_H
-#    include <winsock2.h>
-#  endif
+#  include <winsock2.h>
 #  include <windows.h>
 #endif
 int main(void)
@@ -307,13 +299,11 @@ int main(void)
 
 #ifdef HAVE_SETSOCKOPT_SO_NONBLOCK
 /* includes start */
-#ifdef HAVE_WINDOWS_H
+#ifdef _WIN32
 #  ifndef WIN32_LEAN_AND_MEAN
 #    define WIN32_LEAN_AND_MEAN
 #  endif
-#  ifdef HAVE_WINSOCK2_H
-#    include <winsock2.h>
-#  endif
+#  include <winsock2.h>
 #  include <windows.h>
 #endif
 /* includes start */

CMake/OtherTests.cmake

@@ -29,20 +29,15 @@ set(_source_epilogue "#undef inline")
 
 macro(add_header_include check header)
   if(${check})
-    set(_source_epilogue "${_source_epilogue}\n#include <${header}>")
+    set(_source_epilogue "${_source_epilogue}
+      #include <${header}>")
   endif()
 endmacro()
 
-set(signature_call_conv)
-if(HAVE_WINDOWS_H)
-  set(_source_epilogue
-      "${_source_epilogue}\n#ifndef WIN32_LEAN_AND_MEAN\n#define WIN32_LEAN_AND_MEAN\n#endif")
-  add_header_include(HAVE_WINSOCK2_H "winsock2.h")
-  add_header_include(HAVE_WINDOWS_H "windows.h")
-  set(signature_call_conv "PASCAL")
-  if(WIN32)
-    set(CMAKE_REQUIRED_LIBRARIES "ws2_32")
-  endif()
+if(WIN32)
+  set(CMAKE_EXTRA_INCLUDE_FILES "winsock2.h")
+  set(CMAKE_REQUIRED_DEFINITIONS "-DWIN32_LEAN_AND_MEAN")
+  set(CMAKE_REQUIRED_LIBRARIES "ws2_32")
 else()
   add_header_include(HAVE_SYS_TYPES_H "sys/types.h")
   add_header_include(HAVE_SYS_SOCKET_H "sys/socket.h")
@@ -57,7 +52,7 @@ check_c_source_compiles("${_source_epilogue}
     return 0;
   }" HAVE_MSG_NOSIGNAL)
 
-if(NOT HAVE_WINDOWS_H)
+if(NOT WIN32)
   add_header_include(HAVE_SYS_TIME_H "sys/time.h")
 endif()
 check_c_source_compiles("${_source_epilogue}
@@ -70,9 +65,7 @@ int main(void) {
   return 0;
 }" HAVE_STRUCT_TIMEVAL)
 
-if(HAVE_WINDOWS_H)
-  set(CMAKE_EXTRA_INCLUDE_FILES "winsock2.h")
-else()
+if(NOT WIN32)
   set(CMAKE_EXTRA_INCLUDE_FILES)
   if(HAVE_SYS_SOCKET_H)
     set(CMAKE_EXTRA_INCLUDE_FILES "sys/socket.h")