list.m4: Add some new pthread symbols

Lots of symbols are still missing, but this is required to build mesa as a
result of using pthread-stubs with the latest mesa, specifically:
commit 8aeb6d768b4285f600d09f38d0b406adf46c251d
Author: Rob Herring <robh@kernel.org>
Date:   Tue May 3 21:02:47 2016 -0500

    gbm: Add map/unmap functions

Cc: Rob Clark <robclark@freedesktop.org>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Uli Schlachter <psychon@znc.in>