With the introduction of BOARDSDIR external boards can re-use common
code of BOARDS present in RIOTBASE. To be able to do this file
references may not use $(BOARD) since BOARD will be set by the
external BOARD.
cpu/$(CPU)/Makefile.features and cpu/$(CPU)/Makefile.dep are
automatically included
Part of moving CPU/CPU_MODEL definition to Makefile.features to have it
available before Makefile.include.
DEBUGGER/DEBUGGER_FLAGS/DEBUGSERVER/DEBUGSERVER_FLAGS are evaluated by the
main Makefile.include or by file included by it.
Their value does not need to be exported.
Testing
-------
`git diff --word-diff` only reports `export` being removed.
`git show --stat` reports `55 insertions(+), 55 deletions(-)`
Which is the same amount as lines that where matching
`export[[:blank::]]\+VARIABLE`.
FLASHER and FFLAGS are evaluated by the main Makefile.include or by file
included by it. Their value does not need to be exported.
This will also prevent evaluating 'PORT' for FFLAGS when not needed.
Testing
-------
`git diff --word-diff` only reports `export` being removed.
`git show --stat` reports `84 insertions(+), 84 deletions(-)`
Which is the same amount as lines that where matching
`export[[:blank::]]\+VARIABLE`.
