Can't build libpq test example

Can anyone help me with this problem?

I have installed postgresql-7.2.1 and am trying to compile one of the
test programs from the directory src/test/examples.

I am running an old version of SCO Openserver 5

I am using the following command:

  cc testlibpq.c -I/usr/local/pgsql/include -L/usr/local/pgsql/lib -lpq
-otestlibpq

I receive the following error messages:

undefined                       first referenced
  symbol                             in file
PQfinish                            testlibpq.o
PQsetdbLogin                        testlibpq.o
PQstatus                            testlibpq.o
PQerrorMessage                      testlibpq.o
PQexec                              testlibpq.o
PQresultStatus                      testlibpq.o
PQclear                             testlibpq.o
PQnfields                           testlibpq.o
PQfname                             testlibpq.o
PQgetvalue                          testlibpq.o
PQntuples                           testlibpq.o
ld fatal: Symbol referencing errors. No output written to testlibpq