Indirectly fix hidden mbedtls dependency

scripts.d/50-librist/50-librist.sh

@@ -40,6 +40,11 @@ ffbuild_dockerbuild() {
     meson "${myconf[@]}" ..
     ninja -j"$(nproc)"
     ninja install
+
+    if [[ $TARGET == win* ]]; then
+        # This works around mbedtls not having pkg-config, while recently having added a new dependency.
+        echo "Libs.private: -lbcrypt -lws2_32" >> "$FFBUILD_PREFIX"/lib/pkgconfig/librist.pc
+    fi
 }
 
 ffbuild_configure() {