Postgresql driver for linux ODBC expect a missing pg_config file

Hello,

I want to use postgresql ODBC on linux and forced to compile a new odbc
driver for postgres.
The name of the driver is psqlodbc-09.03.0400.tar.gz

I just did command ./configure and error occurs because 'libpq' is
expected. I search through the file systems and found where libpq.so.*
and libpq.a are stored. After that I did a new command like this:
./configure --with-libpq=/opt/PostgreSQL/9.3/lib/

An error occurs again. The output shows last two lines :
configure: using /usr/local/include /usr/local/lib
configure: error: specified pg_config not found

Please tell me how to continue the compilation ?
The file pg_config exists and is located in /opt/PostgreSQL/9.3/bin/

Note that my postgresql binaries are downloaded directly from the
official site, I did not compile it. Installation directory is
/opt/PostgreSQL/9.3

Thank you