Writing threaded applications requires support from the OS and the language library, in Linux's
case the C library, glibc. Linux's first, widely-used, quasi-POSIX attempt at threads was called
"linuxthreads", and was supplied as part of glibc. Recently, Ingo Molnar and Ulrich Drepper
(both working for RedHat Inc.) studied the "linuxthreads" implementation, found many problems
with it, and started something new called the NPTL (Native POSIX Thread Library). In every
situation NPTL has been found to be superior to the old linuxthreads. NPTL, however, has not
yet been ported to all architectures, in fact it looks like it only works on x86-ish machines.
This is why our compilation above specifies using linuxthreads when building glibc instead of
using the superior NPTL.