From the PR description:
When building on Linux it is possible to create static libraries by
providing a command line option to runConfigureICU. However, when
building using Visual Studio or msbuild we don't use this tool and
so there is no command line option. This change adds a new
configuration (DebugStatic and ReleaseStatic) that links against the
static runtime libraries and thus allows to create static version of
the ICU libraries by selecting the desired configuration.