MSVC 2015 error C2220: warning treated as error

[Luke Benes]

While tracking down the source of the Win 10 SDK issue, I discovered another issue with MSVC 2015. 

After https://cgit.freedesktop.org/libreoffice/core/commit/?id=ed4b23548d28941f9b2c75207832afcb6c6ad0b3

I'm getting the following build error:

[build CXX] sax/source/fastparser/legacyfastparser.cxx
[build PCH] precompiled_configmgr
c:\core\sax\source\fastparser\fastparser.cxx(983) : error C2220: warning treated as error - no 'object' file generated
c:\core\sax\source\fastparser\fastparser.cxx(983) : warning C4702: unreachable code
C:/core/solenv/gbuild/LinkTarget.mk:268: recipe for target 'C:/core/workdir/CxxObject/sax/source/fastparser/fastparser.o' failed
make[1]: *** [C:/core/workdir/CxxObject/sax/source/fastparser/fastparser.o] Error 2
make[1]: *** Waiting for unfinished jobs....
Makefile:259: recipe for target 'build' failed
make: *** [build] Error 2


Do we want to disable warnings treated as errors or to remove the dead code?