The libpq library directory was mentioned here in the wrong place, which

petere · petere · commit 552348c166cf · 2007-01-20T15:26:28.000Z
might lead to a previously installed libpq being used instead.  But we
don't actually have to link with libpq here at all, so remove it.
diff --git a/src/interfaces/ecpg/test/Makefile.regress b/src/interfaces/ecpg/test/Makefile.regress
@@ -3,7 +3,7 @@ override CPPFLAGS := -I../../include -I$(top_srcdir)/src/interfaces/ecpg/include
 override CFLAGS += $(PTHREAD_CFLAGS) 
 
 override LDFLAGS := -L../../ecpglib -L../../pgtypeslib $(LDFLAGS)
-override LIBS := -lecpg -lpgtypes $(libpq) $(LIBS) $(PTHREAD_LIBS)
+override LIBS := -lecpg -lpgtypes $(LIBS) $(PTHREAD_LIBS)
 
 ECPG = ../../preproc/ecpg --regression -I$(srcdir)/../../include
 
@@ -15,4 +15,3 @@ ECPG = ../../preproc/ecpg --regression -I$(srcdir)/../../include
 
 clean:
 	rm -f $(TESTS) $(TESTS:%=%.o) $(TESTS:%=%.c)
-
