Fix corefx altjit test jobs

Fix corefx altjit test jobs

Recently, the corefx build switched from using the VS installed msbuild
to using "dotnet msbuild" for doing builds. This changed the way
command-line parsing was handled.

If we continue to pass the WithoutCategories argument on the command-line,
it ends up requiring an extraordinary number of "escape" backslashes
to preserve exactly the right number of backslashes that will be passed
through to the actual invocation of msbuild. That seems complex and also
not robust to future change.

Instead, construct a response file with the simple required string,
that will be passed directly through to msbuild.

Commit migrated from https://github.com/dotnet/coreclr/commit/aa64317656921a35a4c2b0a30873f780a81ff75a