This introduces make variable NO_PTHREADS for platforms that lack the
support for pthreads library or people who do not want to use it for
whatever reason.  When defined, it makes the multi-threaded index
preloading into a no-op, and also disables threaded delta searching by
pack-objects.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>
Signed-off-by: NMike Ralphson <mike@abacus.co.uk>
Tested-by: Johannes Sixt <j6t@kdbg.org> (AIX 4.3.x)
Signed-off-by: NJunio C Hamano <gitster@pobox.com>