PR/53544: Add a dependency on the Makefile to fix incremental builds.

make sure that nbtools_compat.h is the first thing included for generated files

Simplify.

short circuit lex and yacc rules.

use bootstrap files for yacc too.

switch to new lex

back to old lex

use new lex.

Centralize the definition of the tool name prefix (i.e. "nb") into
bsd.own.mk, as the _TOOL_PREFIX variable.

Prefix all target-specific things with `${MACHINE_GNU_PLATFORM}-'.
Prefix all non-target-specific things with `nb'.

Major overhaul of src/tools and host toolchain. Summary of changes:

* Rewrite src/tools Make logic to work like the rest of the tree wrt
"dependall" and "install". The old "make build" hack is g

Major overhaul of src/tools and host toolchain. Summary of changes:

* Rewrite src/tools Make logic to work like the rest of the tree wrt
"dependall" and "install". The old "make build" hack is gone.

* Remove the MKTOOLS logic. This was linked to the "make build" hack,
and was only needed because TOOLDIR originally had no writable default.

* Redo the GNU configure/make logic to make it fit reasonably in a
BSD make wrapper. Use new ${.ALLTARGETS} variable to scan for
targets in $(srcdir), and mark them with .MADE: to prevent rebuilding.

* Only build cross tools in src/tools; remove some messy logic in
src/usr.* and src/gnu/usr.* that would do target filename rewriting
(improves consistency and readability).

* Add the ability to build cross gdb at tool build time by setting
MKCROSSGDB (default no) to "yes" in mk.conf.

* Add src/tools/groff and set up paths to work with this cross groff.

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Bootstrap toolchain framework, first pass.