devel/gdb: Handle recent 14.0 systems with libc++ in /lib.

[jhb]

Summary

The auto-load python wrapper for libc++ pretty printers has to be
installed at the same path as libc++ to work correctly. Update the
port to install the top-level wrapper in lib/ under the auto-load data
directory instead of usr/lib on recent 14.0 systems.

[emaste]

devel/gdb/Makefile

173

does gdb bulid/work with no libc++ at all?

[pizzamig]

devel/gdb/Makefile

173

no, gdb is a C++ application, so it cannot be built without libc++
I guess the libc++ pretty printer conditions could be reworked/simplified assuming that libc++ is always available.
Is there any possibility that libc++.so.1 is not available?

[emaste]

devel/gdb/Makefile

173

Mmm, I guess it is still possible to build without libc++ right now but see D33108 which avoids libc++ and C++ applications in the base system.

I think it would be fine to remove the .if condition and just require that one of the two paths will exist but it's also fine to just leave tihs.

[jhb]

devel/gdb/Makefile

173

Yeah, when I first added this to the port we still had platforms using GCC instead of clang that didn't support libc++. I could assume it is always present at this point if that is preferred.

[jhb]

I think I'd rather just fix this bit for now and switch to assuming libc++ and always installing these bits as a separate followup.

[emaste]

SGTM