The default version of the compiler toolchain for the engine on Windows is
currently Visual Studio 2019 and MSVC 1.42, so this change sets up Boost
to build using that toolchain, and it adds versions of the compiled binaries
built using that toolchain.
Note that this change does *not* update the Boost Build.cs to look for these
new "vc142" versions of the libraries, nor does it remove the existing "vc141"
versions of the libraries. USD has a link dependency on Boost, so a subsequent
change will rebuild the USD libraries to update the dependencies, after which
it will be safe to remove the old "vc141" Boost libraries.
#rb michael.balzer
#fyi jeanmichel.dignard
#preflight 6116ff37afd67e00019dc839
[CL 17180084 by matt johnson in ue5-main branch]