tools build of 'gdb' fails building texinfo docs

["John D. Baker" <jdbaker%consolidated.net@localhost>]

Followed the instructions in "UPDATING" about cleaning the tools objdir
for 'gdb' (MKCROSSGDB=yes), but builds still fail attempting to build
the "info" documentation (example for mips64el, but seen building sparc
as well:

[...]
/x/current/src/tools/gdb/../../external/gpl3/gdb/dist/gdb/doc/gdb.texinfo:14981: Cross reference to nonexistent node `Tracepoint Packets' (perhaps incorrect sectioning?).
/x/current/src/tools/gdb/../../external/gpl3/gdb/dist/gdb/doc/gdb.texinfo:13568: Cross reference to nonexistent node `qXfer osdata read' (perhaps incorrect sectioning?).
/x/current/src/tools/gdb/../../external/gpl3/gdb/dist/gdb/doc/gdb.texinfo:13566: Cross reference to nonexistent node `Operating System Information' (perhaps incorrect sectioning?).
/x/current/src/tools/gdb/../../external/gpl3/gdb/dist/gdb/doc/gdb.texinfo:13548: Cross reference to nonexistent node `qXfer auxiliary vector read' (perhaps incorrect sectioning?).
/x/current/src/tools/gdb/../../external/gpl3/gdb/dist/gdb/doc/gdb.texinfo:5850: Cross reference to nonexistent node `Agent Expressions' (perhaps incorrect sectioning?).
/x/current/src/tools/gdb/../../external/gpl3/gdb/dist/gdb/doc/gdb.texinfo:2424: Cross reference to nonexistent node `Command and Variable Index' (perhaps incorrect sectioning?).
/x/current/src/tools/gdb/../../external/gpl3/gdb/dist/gdb/doc/gdb.texinfo:194: Menu reference to nonexistent node `Command and Variable Index' (perhaps incorrect sectioning?).
/x/current/src/tools/gdb/../../external/gpl3/gdb/dist/gdb/doc/gdb.texinfo:193: Menu reference to nonexistent node `Concept Index' (perhaps incorrect sectioning?).
/x/current/src/tools/gdb/../../external/gpl3/gdb/dist/gdb/doc/gdb.texinfo:192: Menu reference to nonexistent node `GNU Free Documentation License' (perhaps incorrect sectioning?).
/x/current/src/tools/gdb/../../external/gpl3/gdb/dist/gdb/doc/gdb.texinfo:190: Menu reference to nonexistent node `Copying' (perhaps incorrect sectioning?).
Too many errors!  Gave up.
Too many errors!  Gave up.
nbgmake[3]: *** [gdb.info] Error 1
nbgmake[3]: Leaving directory `/r0/build/current/obj/mips64el/tools/gdb/build/gdb/doc'
nbgmake[2]: *** [subdir_do] Error 1
nbgmake[2]: Leaving directory `/r0/build/current/obj/mips64el/tools/gdb/build/gdb'
nbgmake[1]: *** [all] Error 2
nbgmake[1]: Leaving directory `/r0/build/current/obj/mips64el/tools/gdb/build/gdb'
nbgmake: *** [all-gdb] Error 2
*** Failed target: .build_done
*** In directory: /x/current/src/tools/gdb
*** Failed commands:
	@(cd build && ${BUILD_COMMAND} ${ALL_TARGET})
	=> @(cd build && /usr/bin/env -i AR=ar  AWK=/r0/build/current/tools/amd64/bin/nbawk  CC=cc  CFLAGS=-O  CONFIG_SHELL=/bin/sh  CPPFLAGS=\ -I/r0/build/current/tools/amd64/include  CXX=c++  CXXFLAGS=-O\ -D__STDC_FORMAT_MACROS\ -D__STDC_LIMIT_MACROS\ -D__STDC_CONSTANT_MACROS  INSTALL=/r0/build/current/tools/amd64/bin/mips64el--netbsd-install\ -c\ -p\ -r  LDFLAGS=  LEX=/r0/build/current/tools/amd64/bin/nblex  FLEX=/r0/build/current/tools/amd64/bin/nblex  M4=/r0/build/current/tools/amd64/bin/nbm4  MAKE=/r0/build/current/tools/amd64/bin/nbgmake  PATH="/r0/build/current/tools/amd64/bin:$PATH"  RANLIB=ranlib  YACC=/r0/build/current/tools/amd64/bin/nbyacc am_cv_func_iconv=no MACHINE= BISON=true DESTDIR= INSTALL=/r0/build/current/tools/amd64/bin/mips64el--netbsd-install\ -c\ -p\ -r V=1 /r0/build/current/tools/amd64/bin/nbgmake -j 5 -e MACHINE= BISON=true DESTDIR= INSTALL=/r0/build/current/tools/amd64/bin/mips64el--netbsd-install\ -c\ -p\ -r V=1 all-gdb)
	@if [ ! -f $@ ] || [ -n "$$(find build -type f -newer .build_done -print)" ];  then touch $@; fi
	=> @if [ ! -f .build_done ] || [ -n "$(find build -type f -newer .build_done -print)" ];  then touch .build_done; fi
*** [.build_done] Error code 2

[...]

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