configure.ac: add pthreadstubs support

Add pthreadstubs to avoid pulling in full pthreads library. GBM will be the
first user.

Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
1 file changed