configure.ac: bail out if guix and sed are not detected

Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@cyberdimension.org>

configure.ac

@@ -21,7 +21,12 @@ AC_PROG_MKDIR_P
 AM_INIT_AUTOMAKE([foreign])
 
 AC_CHECK_PROG([GUIX], [guix], [guix])
+AS_IF([test x"$GUIX" = x""],
+      [AC_MSG_ERROR([guix was not found in PATH ($PATH)])])
+
 AC_CHECK_PROG([SED], [sed], [sed])
+AS_IF([test x"$SED" = x""],
+      [AC_MSG_ERROR([sed was not found in PATH ($PATH)])])
 
 AC_SUBST([DOMAIN], [])
 AC_SUBST([ENABLE_WIREGUARD], [])