Update intree gdb/kgdb to handle 2 dwarf types:
DW_OP_GNU_uninit
DW_OP_piece

This squashes the warnings about type 0x93 not known in kgdb when opening a kernel crash dump.

Upstream refs:
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=87808bd699575a850139a1f916512ab7a47fd496
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=42be36b328ae784ae6981da7c7cab95b67ed7737
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=23572ecadc89af384c1804ad7692f32c55fbfc80

Differential Revision: https://reviews.freebsd.org/D2534
Reviewed by: emaste, jhb, davide