contrib/asv.conf.json

setup: unconditionally enable the `long-paths-support` option on Windows

I don't see anything talking about why this was experimental in the first place,
but maybe it was concern about the level of python2 support for it.  But now,
both `python.exe` and the PyOxidizer build of `hg.exe` have a manifest that
enables it, so leaving it off would mean some Mercurial installations could
operate on a repo with long paths, and others couldn't.  Note that only the wide
character functions (XxxW) will have the length restriction lifted.

Sadly, distutils applies `/MANIFEST:EMBED` to the linker in a way that can't
easily be turned off, so we can't use `/MANIFESTFILE` with `extra_preargs` on
`link_executable`.  Fortunately, the compiler object provides a path to the
`mt.exe` it found during initialization, because the previous incarnation seems
to have assumed it is being run within an activated Visual Studio environment.
That causes MSYS builds to fail, and probably would have broke the CI
environment.

{
    "version": 1,
    "project": "mercurial",
    "project_url": "https://mercurial-scm.org/",
    "repo": "..",
    "branches": ["default", "stable"],
    "environment_type": "virtualenv",
    "show_commit_url": "https://www.mercurial-scm.org/repo/hg/rev/",
    "benchmark_dir": "benchmarks",
    "env_dir": "../.asv/env",
    "results_dir": "../.asv/results",
    "html_dir": "../.asv/html"
}