Enables s390x.
A bug was introduced in dotnet7 that causes issues with parallel restore operations when using mono-flavored runtime. A workaround on s390x is setting /p:RestoreParallelDisable=true. While this should work on ppc64le, it doesn't as the bug on that platform seems to affect other kinds of parallel operations (i.e. publishing). There doesn't seem to be a setting to disable parallel publishing, thus ppc64le is still broken.
This MR thus enables that flag when building on s390x, and adds patches that allow the flag to flow through the build process.
See https://github.com/dotnet/runtime/issues/77364
This MR also fixes the bug where dotnet7-build could not build using itself by disabling composite generation during build of aspnetcore.