The assumption in using std::size_t is that every acquisition can be associated
with a unique memory location in the local address space, so the counter cannot
overflow.

Change-Id: I0d004a81d9bf52cf07d13481d9024fcc10b6db6d
Reviewed-on: https://gerrit.libreoffice.org/41580Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>