Revert "ecpg: Don't link compatlib with libpq"

This reverts commit 3780fc67.

HP-UX didn't like it.  There would probably be a way to fix that, but
since the net effect of all of this is zero because ecpg ends up using
libpq anyway, it's not worth bothering further.

src/interfaces/ecpg/compatlib/Makefile

@@ -21,7 +21,7 @@ override CPPFLAGS := -I../include -I$(top_srcdir)/src/interfaces/ecpg/include \
 	-I$(libpq_srcdir) -I$(top_srcdir)/src/include/utils $(CPPFLAGS)
 override CFLAGS += $(PTHREAD_CFLAGS)
 
-SHLIB_LINK = -L../ecpglib -lecpg -L../pgtypeslib -lpgtypes \
+SHLIB_LINK = -L../ecpglib -lecpg -L../pgtypeslib -lpgtypes $(libpq) \
 	$(filter -lintl -lm, $(LIBS)) $(PTHREAD_LIBS)
 SHLIB_PREREQS = submake-ecpglib submake-pgtypeslib