[3.5] bpo-31095: fix potential crash during GC

[methane]

(cherry picked from commit a6296d3)

https://bugs.python.org/issue31095

[larryhastings]

Hi, Steve, this is failing on link, can you look in to it?

[methane]

Link error message in AppVeyor:

[00:03:36]   Finished generating code
[00:03:37]      Creating library C:\projects\cpython\PCBuild\win32\_elementtree.lib and object C:\projects\cpython\PCBuild\win32\_elementtree.exp
[00:03:37] xmlparse.obj : error LNK2001: unresolved external symbol __Expat_LoadLibrary [C:\projects\cpython\PCbuild\_elementtree.vcxproj]
[00:03:37] C:\projects\cpython\PCBuild\win32\_elementtree.pyd : fatal error LNK1120: 1 unresolved externals [C:\projects\cpython\PCbuild\_elementtree.vcxproj]

[zooba]

Looks like the pyexpat.vcxproj file was never updated with the last update, and whoever merged that updated didn't run appveyor (or they ignored the failure).

I'll send a PR to update the file. Looks like 3.6 got the change okay, so guessing it's just 3.5.

[zooba]

See #3751 for the fix.