Use pkg-config to find libgcrypt.

--- bitlbee-3.6/configure	2019-02-07 19:53:38.000000000 +0000
+++ bitlbee-3.6/configure	2025-07-04 04:44:21.389286087 +0100
@@ -402,8 +402,8 @@
 {
 	if $PKG_CONFIG --exists gnutls; then
 		cat <<EOF >>Makefile.settings
-EFLAGS+=$($PKG_CONFIG --libs gnutls) $(libgcrypt-config --libs)
-CFLAGS+=$($PKG_CONFIG --cflags gnutls) $(libgcrypt-config --cflags)
+EFLAGS+=$($PKG_CONFIG --libs gnutls libgcrypt)
+CFLAGS+=$($PKG_CONFIG --cflags gnutls libgcrypt)
 EOF
 		ssl=gnutls
 		if ! $PKG_CONFIG gnutls --atleast-version=2.8; then