Temporary attempt at a workaround for further MSVC restrict build failures.

Temporary attempt at a workaround for further MSVC restrict build failures.

It appears some versions of msvc use __declspec(restrict) in stdlib.h
and subsidiary headers. Including those after defining 'restrict' to
'__restrict' doesn't work.  Try to get the buildfarm green to see
whether there's further problems, by including stdlib.h just before
said define.