There was a check in linux.cf for the Linux libc version that didn't
work, since these were never set anywhere. Presumably current Xorg
imake sets these, but since we aren't using that... (yet)
As a result, the build assumed that thread-safe API's were not
supported. Setting the default libc major version to '6' allows the
proper build to take place. libc5 was never threadsafe and no one has
probably used it in over 10 years.
As a result, some earlier porting fixes that referenced '__fds_bits'
on linux systems had to be reverted as these are not valid in an MT
environment. They are also not neccessary when building in such an
environment, as the normal 'fds_bits' works fine.
This patch defintely needs testing on many linux systems.
Peter Howkins