BUG #12884: configure script fails on a platform with /tmp directory read only

The following bug has been logged on the website:

Bug reference:      12884
Logged by:          X
Email address:      pgconfbug@yopmail.com
PostgreSQL version: 9.0.19
Operating system:   Linux SLES 10 SP2
Description:

On a platform intentionally setup with a /tmp directory readonly but with a
TMPDIR environment variable pointing to a writable location the configure
script fails detecting a non thread safe platform.

Reading of config.log indicates a write failure in /tmp directory for
execution of thread safety conftest program.
The corresponding source is src/test/thread/thread_test.c

The reading of the source shows that this test program explicitly references
/tmp for writing instead of using a TMPDIR capable function like tempnam()

Replacement of hard coded /tmp reference by a suitable value allows
configure to complete sucessfully.

The "make" and "make install" are also OK.