Do not add -I$prefix flag when looking for any lib. There are no headers there.

Part of:

https://github.com/uniconproject/unicon/commit/bb8861db956a206d5f8f058e57346b8173986ad9
--- aclocal.m4.orig	2026-03-31 07:06:59.000000000 -0500
+++ aclocal.m4	2026-03-31 07:11:26.000000000 -0500
@@ -69,7 +69,7 @@
 [
 if test  x$2 != "x"
 then
-	save_flags([-I$2/include -I$2], [-L$2/lib], [])
+	save_flags([-I$2/include], [-L$2/lib], [])
 else
 	save_flags([], [], [])
 fi