Treat MSVC warning C4910 and C4003 as errors in the CI builds
Looking at the proposed changes for ICU-9749, an additional warning is now being generated in the MSCV builds.
The warning is:
However, I believe that this warning should be an error. (This will cause ICU to fail to build for us internally).
With ICU-20200, we now treat a limited subset of warnings as errors for MSVC, two of which are for DLL exports or explicit template instantiations.
(Ex: C4661 "No suitable definition provided for explicit template instantiation request" as an error.)
I believe we should add this warning (C4910) to the list of errors as well.
Per ICU-TC call on 2019-03-27, will take this to make both 4910 and 4003 errors.
We should likely also treat C4003 as an error too (See ICU-20516).