Exported header files used by applications should allow the strictest
compiler flags. Language extensions used in many places must be explicitly
marked to avoid warnings and compilation failures.
Unnamed structs/unions are allowed since C11, however many compiler
versions do not use this mode by default.
This commit prevents the following errors:
error: ISO C99 doesn't support unnamed structs/unions
error: struct has no named members
Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>