[riot-notifications] [RIOT-OS/RIOT] makefiles: Add -fwrapv to CFLAGS (#10748)

Marian Buschsieweke notifications at github.com
Thu Jan 10 15:13:35 CET 2019

### Contribution description

This commit makes overflow of signed integers to behave as expected by at 90%
of the C developers, even though overflow of signed integers are strictly
undefined behavior.

Note: Please do not add code relying on a specific behavior for the overflow of
      signed integers, even though `-fwrpav` will make that code work. This is
      intended to mitigate the risk of bugs in overflow checks being exploited,
      not to encourage adding new bugs.

See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=30475 for details and see
http://c-faq.com/misc/intovf.html on how to implement overflow checks properly.

Put here the description of your contribution:
- describe which part(s) of RIOT is (are) involved
- if it's a bug fix, describe the bug that it solves and how it is solved
- you can also give more information to reviewers about how to test your changes

### Testing procedure

I guess if Murdock still compiles everything, this should be sufficient

### Issues/PRs references

This issue was discussed in https://github.com/RIOT-OS/RIOT/pull/10740, but that PR is not much related otherwise
You can view, comment on, or merge this pull request online at:


-- Commit Summary --

  * makefiles: Add -fwrapv to CFLAGS

-- File Changes --

    M makefiles/cflags.inc.mk (11)

-- Patch Links --


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