chore: ensure libpq libdir is found by the linker

Signed-off-by: Leonardo Cecchi <leonardo.cecchi@enterprisedb.com>

Author: leonardoce

Makefile

@@ -1,5 +1,5 @@
 http_test: http_test.cpp
-	clang++ -o http_test -std=c++17 http_test.cpp -I$$(pg_config --includedir) $$(pg_config --ldflags) -lpq -lpthread
+	clang++ -o http_test -std=c++17 http_test.cpp -I$$(pg_config --includedir) $$(pg_config --ldflags) -L$$(pg_config  --libdir) -lpq -lpthread
 
 fmt:
 	clang-format -i http_test.cpp