c-recognize-typeless-decls is a variable defined in `cc-engine.el'.
Its value is

  • Automatically becomes buffer-local when set.

Non-nil means function declarations without return type should be
recognized. That can introduce an ambiguity with parenthesized macro
calls before a brace block. This setting does not affect declarations
that are preceded by a declaration starting keyword, so
e.g. `c-typeless-decl-kwds' may still be used when it's set to nil.