It looks like there's something wrong on your system. For somewhat reason the configure script did pass the test for lo_import_with_oid (added in 8.4), but when compiling and linking an old version of libpq is used.

Could you please identify what versions of the headers and libpq are installed on your system?

E.g.
locate libpq-fe.h
locate libpq.so

It also would be useful to know if they were installed from a Ubuntu package or compiled by you.

No feedback was provided for this bug for over a week, so it is
being suspended automatically. If you are able to provide the
information that was originally requested, please do so and change
the status of the bug back to "Open".

Version 5.3.0:

ext/pgsql/.libs/pgsql.o: In function `zif_pg_lo_import':
/path/ext/pgsql/pgsql.c:3381: undefined reference to `lo_import_with_oid'
collect2: ld returned 1 exit status
make: *** [sapi/cli/php] Error 1

Version 5.2.10:

Build complete.
Don't forget to run 'make test'.

Version 5.3.0:

ext/pgsql/.libs/pgsql.o: In function `zif_pg_lo_import':
/path/ext/pgsql/pgsql.c:3381: undefined reference to `lo_import_with_oid'
collect2: ld returned 1 exit status
make: *** [sapi/cli/php] Error 1

Version 5.2.10:

Build complete.
Don't forget to run 'make test'.

I've only found this to be a problem on multi architectured platforms.  Because some of the PHP build system is based on file testing and not feature testing, it looks for files in some places without verifying if they work.  For example, by compiling with ./configure --libdir=/usr/lib64 will still for some reason test for /usr/lib/libmysqlclient.so and thereby add -L/usr/lib to the library path and if you have a different version of the postgres librarys in there, it'll try to use them.  The really weird thing, is that it correctly compiles it for the configure test script, but fails when trying to do the actual build.  I've had to manually edit the Makefile and replace /usr/lib's with /usr/lib64's