trivial diff: Include <errno.h> in mercury_trace_base.c

[Mark Anthony BROWN]

Hi,

This avoids a compilation error when MR_TRACE_HISTOGRAM is set.

Estimated hours taken: 0.1

runtime/mercury_trace_base.c:
	Include <errno.h> for use when MR_TRACE_HISTOGRAM is defined.

Index: runtime/mercury_trace_base.c
===================================================================
RCS file: /home/mercury1/repository/mercury/runtime/mercury_trace_base.c,v
retrieving revision 1.7
diff -u -t -u -r1.7 mercury_trace_base.c
--- mercury_trace_base.c	1998/11/10 13:39:59	1.7
+++ mercury_trace_base.c	1998/11/19 05:39:02
@@ -24,6 +24,7 @@
 #include "mercury_misc.h"
 #include <stdio.h>
 #include <unistd.h>             /* for the write system call */
+#include <errno.h>
 
 /*
 ** Do we want to use the debugger within this process, or do want to use