Don't suppport use --project=compile_commands.json
add script to build from source

I believe this will fix the residual issue.

When git merges are in use it appears that --shallow-since=DATE stops at
the first merge commit that is older than DATE. This could create a too
shallow clone that lacks the desired commit. Disable this optimization.
Observed with git 2.19.1.

Fixes #359

OpenSSL 1.1.0i on AppVeyor does not include applink.c, so copy it from
OpenSSL 1.0.2p (which has lib\VC\libeay32MD.lib, but not libcrypto.lib).

The weird "2>&1" redirection for git clone tries to prevent PS from
printing a RemoteException (NativeCommandError) from using stderr.

CI needs a fixed environment. Fix picotls at a know commit. A change to that commit will be its own PR and own CI run.