make: buildtest with "-Wall -Wextra -Werror"

[Kijewski]

DO NOT MERGE UNTIL ALL WARNINGS ARE FIXED IN MASTER

With almost all warnings fixed or at least being addressed in an open PR, I think we should strive to keep it that way.

This PR makes buildtest more pedantic by supplying -Wall -Wexta -Werror by default.
This can be disabled through make W_ALL=0 W_EXTRA=0 W_ERROR=0, resp., or with make W_NONE=1, which disables every extra flag.
With make PEDANTIC=1 PEDANTIC_ERRORS=1 you can make the buildtest even more pedantic.

Also the generic make variable W_FLAGS is added, through which extra CFLAGS can be supplied in the normal make all.

For non-buildtest builds you can supply W_NONE=0 and/or the individual flags,
too

[mehlis]

+1 to have this PR merged until next release (make it a release goal)

[LudwigKnuepfer]

Please rebase

[Kijewski]

Rebased.

[LudwigKnuepfer]

Please rebase.

[Kijewski]

Rebased.

[Kijewski]

Rebased.

[OlegHahm]

I don't think we can achieve this for the upcoming release already. Postponed.

[miri64]

How's the status on this front?

[LudwigKnuepfer]

Master still has issues.

[miri64]

Closed as memo for now. Reopen if you object.

[OlegHahm]

What's the reason for closing?

[jnohlgard]

I would like to see the CI build without warnings as a long term goal.

[miri64]

(fails already for the new power management T.T)

[miri64]

=> postponed I guess.

[OlegHahm]

Not sure this is so easy, since the build fails after the first warning - which happens rather early on most platforms except native.

Well it is easy, just tedious ;-)

And how would you do it?

[miri64]

And how would you do it?

Same way we did cppcheck?

[miri64]

So should we tackle this for 2017.07?

[Kijewski]

So should we tackle this for 2017.07?

How about CFLAGS += -Wall -Wextra -Werror in ./{core,sys,drivers}/Makefile? Might be a better approach than my PR, as it "allows" the user to continue writing ugly application code. Also we could tackle one directory after another without having to fix everything at once.

[jnohlgard]

@Kijewski

How about CFLAGS += -Wall -Wextra -Werror in ./{core,sys,drivers}/Makefile?

... and in boards/ and cpu/

[aabadie]

A good candidate for 2017.07? @miri64 @Kijewski ?

Needs rebase btw

[miri64]

Conventional pre-release ping. ;-)

[smlng]

I suggest to close as memo as it is not mergeable anymore and use #7919 as a replacement.

[Kijewski]

Closed as memo because the original author is lazy.