fix calling conventions

When a function is assigned to a function pointer that is declared
with a particular calling convention, then the assigned function
must be declared with that calling convention as well.  Otherwise,
kaboom!!!

The following functions are fixed by this change:

kuser/kx509.c
  validate1()
  add1_2chain()

lib/base/log.c
  log_syslog()
  close_syslog()
  log_file()
  close_file()

lib/gssapi/mech/context.c
  gss_set_log_function()

lib/krb5/kx509.c
  certs_export_func()

Change-Id: Ib68abf739e3385e98136fa4e4f5a0240e9fce033

lib/gssapi/mech/context.c

@@ -231,7 +231,7 @@ gss_mg_set_error_string(gss_OID mech,
 static void *log_ctx = NULL;
 static void (*log_func)(void *ctx, int level, const char *fmt, va_list) = NULL;
 
-void
+void GSSAPI_LIB_CALL
 gss_set_log_function(void *ctx, void (*func)(void * ctx, int level, const char *fmt, va_list))
 {
     if (log_func == NULL) {