toolchain/54286: MKCROSSGDB=yes build fails for dreamcast 8.99.42

[jdbaker%consolidated.net@localhost]

>Number:         54286
>Category:       toolchain
>Synopsis:       MKCROSSGDB=yes build fails for dreamcast 8.99.42
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    toolchain-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Jun 07 16:40:00 +0000 2019
>Originator:     John D. Baker
>Release:        target: NetBSD/dreamcast-8.99.42;  host: NetBSD/amd64-8.1_STABLE
>Organization:
>Environment:
host:
NetBSD plex760.technoskunk.fur 8.1_STABLE NetBSD 8.1_STABLE (PLEX760) #101: Mon Jun  3 01:48:08 CDT 2019  sysop%plex760.technoskunk.fur@localhost:/r0/build/netbsd-8/obj/amd64/sys/arch/amd64/compile/PLEX760 amd64
>Description:
After the new GDB was imported and everyone switched to it, building
for dreamcast with MKCROSSGDB=yes fails as follows:

[...]
  CXX    sh-nbsd-tdep.o
/x/current/src/tools/gdb/../../external/gpl3/gdb/dist/gdb/sh-nbsd-tdep.c:35:24: fatal error: gdb_assert.h: No such file or directory
compilation terminated.
nbgmake[1]: *** [sh-nbsd-tdep.o] Error 1
nbgmake[1]: Leaving directory `/r0/build/current/obj/dreamcast/tools/gdb/build/gdb'
nbgmake: *** [all-gdb] Error 2
[...]

>How-To-Repeat:
./build.sh -U -m dreamcast -T /r0/build/current/tools/amd64 -O /r0/build/current/obj/dreamcast -D /r0/build/current/DEST/dreamcast -R /r0/build/current/REL -X ../xsrc -x -u -V MKCROSSGDB=yes tools
>Fix: