curl_gssapi: Guard files with HAVE_GSSAPI.

Bug: http://curl.haxx.se/mail/lib-2011-07/0074.html
Reported and fix suggested by: Ben Greear

lib/curl_gssapi.c

@@ -20,6 +20,10 @@
  *
  ***************************************************************************/
 
+#include "setup.h"
+
+#ifdef HAVE_GSSAPI
+
 #include "curl_gssapi.h"
 
 OM_uint32 Curl_gss_init_sec_context(
@@ -46,3 +50,5 @@ OM_uint32 Curl_gss_init_sec_context(
                               ret_flags,
                               NULL /* time_rec */);
 }
+
+#endif /* HAVE_GSSAPI */

lib/curl_gssapi.h

@@ -22,6 +22,8 @@
 
 #include "setup.h"
 
+#ifdef HAVE_GSSAPI
+
 #ifdef HAVE_GSSGNU
 #  include <gss.h>
 #elif defined HAVE_GSSMIT
@@ -45,3 +47,5 @@ OM_uint32 Curl_gss_init_sec_context(
     gss_buffer_t input_token,
     gss_buffer_t output_token,
     OM_uint32 * ret_flags);
+
+#endif /* HAVE_GSSAPI */