Skip the administrative overhead of using pthreads when only using one
thread. Instead take the non-threaded path which would be taken under
NO_PTHREADS.
The threading support was initially added in commit
5b594f457a ("Threaded grep", 2010-01-25) with a hardcoded compile-time
number of 8 threads. Later the number of threads was made configurable
in commit
89f09dd34e ("grep: add --threads=<num> option and
grep.threads configuration", 2015-12-15).
That change did not add any special handling for --threads=1. Now we
take a slightly faster path by skipping thread handling entirely when
1 thread is requested.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>