[sparc64] Fix missing LIB_DEPENDS for www/sarg

Had a build failure on sparc64

In file included from usage.c:27:
include/conf.h:103:22: error: execinfo.h: No such file or directory

devel/libexecinfo seems to be a hidden dependency. It got picked up as
available during configure.

This fixes it.

ok?

--Kurt

Index: Makefile
===================================================================
RCS file: /cvs/ports/www/sarg/Makefile,v
retrieving revision 1.30
diff -u -r1.30 Makefile
--- Makefile 12 Jul 2019 20:51:05 -0000 1.30
+++ Makefile 27 Sep 2020 16:15:17 -0000
@@ -4,18 +4,19 @@

DISTNAME= sarg-2.3.11
CATEGORIES= www
-REVISION= 1
+REVISION= 2

HOMEPAGE= http://sarg.sourceforge.net/

# GPLv2+
PERMIT_PACKAGE= Yes

-WANTLIB= c gd iconv intl m pcre
+WANTLIB= c gd execinfo iconv intl m pcre

MASTER_SITES= ${MASTER_SITE_SOURCEFORGE:=sarg/}

LIB_DEPENDS= devel/gettext,-runtime \
+ devel/libexecinfo \
devel/pcre \
graphics/gd