pgsql: Refactor the code that creates the shared library export files to

Log Message:
-----------
Refactor the code that creates the shared library export files to appear
only once in Makefile.shlib and not in four copies.

Modified Files:
--------------
    pgsql/src:
        Makefile.shlib (r1.109 -> r1.110)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/Makefile.shlib?r1=1.109&r2=1.110)
    pgsql/src/interfaces/ecpg/compatlib:
        Makefile (r1.38 -> r1.39)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/compatlib/Makefile?r1=1.38&r2=1.39)
    pgsql/src/interfaces/ecpg/ecpglib:
        Makefile (r1.55 -> r1.56)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/ecpglib/Makefile?r1=1.55&r2=1.56)
    pgsql/src/interfaces/ecpg/pgtypeslib:
        Makefile (r1.40 -> r1.41)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/pgtypeslib/Makefile?r1=1.40&r2=1.41)
    pgsql/src/interfaces/libpq:
        Makefile (r1.160 -> r1.161)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/Makefile?r1=1.160&r2=1.161)