Fixtype of function definitions [C17:6.9.1] [C17:A.2.4].
This is a product type introduced by fty::defprod.
This corresponds to function-definition in the grammar in [C17]. Unlike that grammar, we do not constrain the function body to be a compound statement in this fixtype.
As a GCC extension,
we include the possibility that
the function definition starts with the
We also allow an optional assembler name specifier and zero or more attribute specifiers, as GCC extensions; see the ABNF grammar.