TSAN patches

Submitted by Colin Walters @walters

Link to original bug (#774645)

Description

I'm trying to use -fsanitize=thread for OSTree, and some of these issues seem to go into GLib. Also, the sanitizers work better if the userspace libraries are built with them too.

This fix is similar to https://github.com/ostreedev/ostree/pull/582/commits/b6814bb37cacd7a36715cf91766eb760b1b33c66

Mixing atomic and non-atomic reads trips TSAN, so let's change the assertions to operate on the local values returned from atomic read/writes.

Without this change I couldn't even build GLib with TSAN, since we use gresources during compilation, which uses GSubprocess, which hits this code.