curl: Never consider using Windows APIs on Cygwin

Our Windows API header checks are conditioned on if(NOT UNIX) but
libarchive checks HAVE_WINDOWS_H anyway so the result leaks into
the cache and influenes the curl build.  Set the check results to
false explicitly for curl when not on Windows to tolerate this.

Reported-by: Vyacheslav Karpukhin <[email protected]>

Utilities/cmcurl/CMakeLists.txt

@@ -524,12 +524,18 @@ check_include_file("features.h"       HAVE_FEATURES_H)
 if(NOT UNIX)
   check_include_file_concat("ws2tcpip.h"     HAVE_WS2TCPIP_H)
   check_include_file_concat("winsock2.h"     HAVE_WINSOCK2_H)
-endif(NOT UNIX)
+else()
+  set(HAVE_WS2TCPIP_H 0)
+  set(HAVE_WINSOCK2_H 0)
+endif()
 check_include_file_concat("stdio.h"          HAVE_STDIO_H)
 if(NOT UNIX)
   check_include_file_concat("windows.h"      HAVE_WINDOWS_H)
   check_include_file_concat("winsock.h"      HAVE_WINSOCK_H)
-endif(NOT UNIX)
+else()
+  set(HAVE_WINDOWS_H 0)
+  set(HAVE_WINSOCK_H 0)
+endif()
 
 check_include_file_concat("inttypes.h"       HAVE_INTTYPES_H)
 check_include_file_concat("sys/filio.h"      HAVE_SYS_FILIO_H)