64-bit Windows build failure after MSVC Update

[Luke Benes]

After I updated from MSVC 15.7.6 to 15.8.1, I started seeing the following build failure:

[build CXX] sc/source/ui/docshell/docsh8.cxx
c:\core\sc\source\ui\docshell\docsh8.cxx(996) : error C2220: warning treated as error - no 'object' file generated
c:\core\sc\source\ui\docshell\docsh8.cxx(996) : warning C4702: unreachable code
c:\core\sc\source\ui\docshell\docsh8.cxx(1054) : warning C4702: unreachable code
c:\core\sc\source\ui\docshell\docsh8.cxx(1063) : warning C4702: unreachable code
make[1]: *** [C:/core/solenv/gbuild/LinkTarget.mk:293: C:/core/workdir/CxxObject/sc/source/ui/docshell/docsh8.o] Error 2
make[1]: *** Waiting for unfinished jobs....
make: *** [Makefile:286: build] Error 2


This only seems to affect 64-bit release builds. 32-bit release builds are working. This is similar to 

http://document-foundation-mail-archive.969070.n3.nabble.com/Windows-32-bit-build-failure-unreachable-code-td4243848.html#a4244013