hadrian: Build with threaded runtime if available

In #16873 (closed) it has been observed that if the boostrapping compiler does not support a threaded runtime, then a build fails. Since !1299 (closed) a warning is printed to stdout if hadrian fails and if the bootstrapping compiler does not support a threaded runtime:

Your compiler does not support the threaded runtime system.
Please disable the \`threaded\` Cabal flag in project.cabal.local
by running:

    echo -e "package hadrian\n  flags: -threaded" >> project.cabal.local

The warning is printed independently whether a file cabal.project.local with the appropriate flag disabled exists or not. For example, running the testsuite with a failing testcase results in the warning printed.

In contrast to !1299 (closed) this patch tries to detect whether the bootstrapping compiler supports a threaded runtime and depending on this passes a flag to cabal omitting the need to create a local file.