configure: add --sysconfdir / $SYSCONFDIR handling

so that we don't have to hardcode /etc in gmid.c.  Helps on systems
like FreeBSD where the non-base programs are expected to look for
their config in /usr/local/etc.

configure

@@ -50,6 +50,7 @@ fi
 
 INSTALL=${INSTALL-install}
 PREFIX=${PREFIX-/usr/local}
+SYSCONFDIR=${SYSCONFDIR-/etc}
 
 CDIAGFLAGS=
 CDIAGFLAGS="${CDIAGFLAGS} -W -Wall -Wextra -Wpointer-arith -Wuninitialized"
@@ -100,6 +101,7 @@ while [ $# -gt 0 ]; do
 	--bindir)	key=BINDIR ;;
 	--mandir)	key=MANDIR ;;
 	--prefix)	key=PREFIX ;;
+	--sysconfdir)	key=SYSCONFDIR ;;
 	--with-libtls)	key=LIBTLS ;;
 	esac
 
@@ -120,6 +122,7 @@ while [ $# -gt 0 ]; do
 	LDFLAGS)	LDFLAGS="$val" ;;
 	PKG_CONFIG)	PKG_CONFIG="$val" ;;
 	PREFIX)		PREFIX="$val" ;;
+	SYSCONFDIR)	SYSCONFDIR="$val" ;;
 	YACC)		YACC="$val" ;;
 	*)		usage
 	esac
@@ -437,6 +440,10 @@ cat <<__HEREDOC__
 #define DISABLE_SANDBOX		${DISABLE_SANDBOX}
 #define HAVE_LANDLOCK		${HAVE_LANDLOCK}
 
+#ifndef SYSCONFDIR
+# define SYSCONFDIR		"${SYSCONFDIR}"
+#endif
+
 __HEREDOC__
 
 if [ ${HAVE_ENDIAN_H} -eq 1 ]; then

gmid.c

@@ -68,7 +68,7 @@ int pidfd = -1;
 
 int debug, verbose;
 
-const char *config_path = "/etc/gmid.conf";
+const char *config_path = SYSCONFDIR "/gmid.conf";
 const char *pidfile;
 
 static void