Update Solution.pm for HAVE_GSSAPI[_GSSAPI]_EXT_H, too.

Commit d48ac00 was still a brick shy of a load.
Per buildfarm (via Andrew Dunstan).

Discussion: https://postgr.es/m/08dd6053-deee-52e9-954b-eb69232905c9@dunslane.net

Author: tglsfdc

src/tools/msvc/Solution.pm

@@ -262,6 +262,8 @@ sub GenerateFiles
 		HAVE_GETOPT_LONG                            => undef,
 		HAVE_GETPEEREID                             => undef,
 		HAVE_GETPEERUCRED                           => undef,
+		HAVE_GSSAPI_EXT_H                           => undef,
+		HAVE_GSSAPI_GSSAPI_EXT_H                    => undef,
 		HAVE_GSSAPI_GSSAPI_H                        => undef,
 		HAVE_GSSAPI_H                               => undef,
 		HAVE_HMAC_CTX_FREE                          => undef,