TS-4560: Fix C++ API shared_ptr detection.

[jpeach]

Since ink_autoconf.h is not installed, we can't use it to figure
out which shared_ptr implementation to use. Further, Traffic Server
might not have been built with the same toolchain that 3rd party
plugins are using.

Since shared_ptr is used in the C++ API headers, both Traffic Server
and the plugins need to agree on which implementation to use. The
best (but not perfect) solution is to hardcode it into the header
file during the Traffic Server build. This means that both parties
are consistent and any remaining problems could be attributed to
C++ standard library compatibility.

[jpeach]

Ping @bgaff @SolidWallOfCode

[atsci]

FreeBSD build failed! See https://ci.trafficserver.apache.org/job/Github-FreeBSD/295/ for details.

[atsci]

Linux build successful! See https://ci.trafficserver.apache.org/job/Github-Linux/187/ for details.

[zwoop]

Not sure why the FreeBSD build failed, trying again. [approve ci]

[atsci]

FreeBSD build successful! See https://ci.trafficserver.apache.org/job/Github-FreeBSD/296/ for details.

[atsci]

Linux build successful! See https://ci.trafficserver.apache.org/job/Github-Linux/188/ for details.

[jpeach]

we should do the same with all the ink config stuff rather than including ink_config

I'm not sure what you mean by this. This patch is removing ink_autoconf.h from the public C++ API.

[bgaff]

Sorry I was referring specifically to the config ( the txn config set enums ) but I think this solves that too.

Please land this, thanks for doing it!