[RFA v3 0/2] Make line tables independent of progspace

[Tom Tromey]

This is version 3 of my patch to make line tables independent of
progspace.

Version 2 was here:

https://sourceware.org/ml/gdb-patches/2018-03/msg00385.html

I think this version addresses all the review comments, but of course
careful review is still required.  This version implements the
"unrelocating" idea to speed up find_pc_sect_line.

Regression tested by the buildbot.

Tom