cmake: pre-cache HAVE_BASENAME for mingw-w64 and MSVC

`basename` is present in mingw-w64, missing from MSVC. Pre-cache
accordingly to make configure faster.

Notice that `basename` has a bug so we later disable it even with
mingw-w64:
781242ffa4/lib/curl_setup.h (L820-L825)

Closes #11974

CMake/Platforms/WindowsCache.cmake

@@ -33,6 +33,7 @@ if(NOT UNIX)
       set(HAVE_UNISTD_H 1)
       set(HAVE_INTTYPES_H 1)
       set(HAVE_STRTOLL 1)
+      set(HAVE_BASENAME 1)
     elseif(MSVC)
       if(NOT MSVC_VERSION LESS 1800)
         set(HAVE_INTTYPES_H 1)
@@ -46,6 +47,7 @@ if(NOT UNIX)
       else()
         set(HAVE_SNPRINTF 0)
       endif()
+      set(HAVE_BASENAME 0)
     endif()
 
     set(HAVE_LIBSOCKET 0)