Add a temp-install prerequisite to src/interfaces/ecpg "checktcp".

The target failed, tested $PATH binaries, or tested a stale temporary
installation.  Commit c66b438d missed
this.  Back-patch to v10 (all supported versions).

src/interfaces/ecpg/Makefile

@@ -26,5 +26,6 @@ install-ecpglib-recurse: install-pgtypeslib-recurse
 clean distclean maintainer-clean:
 	$(MAKE) -C test clean
 
+checktcp: | temp-install
 check checktcp installcheck:
 	$(MAKE) -C test $@