devel/gdb: Upgrade to gdb 8.1

[pizzamig]

Summary

Initial work to upgrade gdb to version 8.1

Currently, it build correctly if kgdb is disabled
kgdb code has to be ported to gdb 8.1
It looks to me that fbsd-kvm.c and fbsd-kld,c needs to be ported to use lm_info_base instead of lm_info

[jhb]

That was quick! I'll work on forward-porting kgdb in the next few days.

[jhb]

• Update the kgdb bits for 8.1.
• Backport some patches comitted upstream to GDB post 8.1. One set of patches adds support for 'info proc' on both live processes and core dumps. Another set are some fixes that fixed about 20 test failures in GDB's test suite.
• Explicitly override the osabi for kgdb so that kgdb will work when only the symbols file for a kernel is used.

[jhb]

Sorry for the delay. Hope it is ok that I uploaded a modified version of your previous patch. I only changed kgdb bits and added the commits I mentioned above ('info proc', etc.). The changes for 8.1 (in case the logs are any help with composing the port commit log) are here: https://github.com/bsdjhb/gdb/compare/510a598...freebsd-8.1-kgdb

[jhb]

• Unwind syscall trapframes in PTI kernels properly ("fast_syscall_common").