RFR: Make Serviceability Agent attach functionality optional

[Mikael Vidstedt]

FYI: I messed up the details of the patch. Working on fixing it.

Cheers,
Mikael

> On Apr 13, 2017, at 9:19 AM, Mikael Vidstedt <mikael.vidstedt at oracle.com> wrote:
> 
> 
> The Serviceability Agent (aka. SA) has functionality to attach to running processes forcefully/without the cooperation of the VM, allowing “live” debugging even when the processes is stuck. On linux the implementation relies on the functionality provided by the thread_db.h header file.
> 
> musl doesn’t support thread_db.h (or any other thread debugging library for that sake). This patch makes the inclusion of the attach/live debugging support optional, and only includes it if the thread_db.h header file is available.
> 
> Note that the core debugging functionality still works without the attach/live debugging functionality in the SA (at least in theory, I haven’t taken core debugging for a spin yet).
> 
> top: http://cr.openjdk.java.net/~mikael/webrevs/portola/sathreaddb/webrev.00/webrev/
> hotspot: http://cr.openjdk.java.net/~mikael/webrevs/portola/sathreaddb/webrev.00/hotspot/webrev/
> 
> Cheers,
> Mikael
>