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/base/log.c

@@ -159,7 +159,7 @@ struct _heimdal_syslog_data{
     int priority;
 };
 
-static void
+static void HEIM_CALLCONV
 log_syslog(heim_context context, const char *timestr,
            const char *msg, void *data)
 {
@@ -167,7 +167,7 @@ log_syslog(heim_context context, const char *timestr,
     syslog(s->priority, "%s", msg);
 }
 
-static void
+static void HEIM_CALLCONV
 close_syslog(void *data)
 {
     free(data);
@@ -209,7 +209,7 @@ struct file_data {
     int freefilename;
 };
 
-static void
+static void HEIM_CALLCONV
 log_file(heim_context context, const char *timestr, const char *msg, void *data)
 {
     struct timeval tv;
@@ -274,7 +274,7 @@ out:
     }
 }
 
-static void
+static void HEIM_CALLCONV
 close_file(void *data)
 {
     struct file_data *f = data;