This eliminates some simple-declaration/function-definition false
parses.
- implement a function to determine whether a declarator ForestNode is a
function declarator;
- extend the standard declarator to two guarded function-declarator and
non-function-declarator nonterminals;
Differential Revision: https://reviews.llvm.org/D129222
I expect to eliminate this ambiguity at the grammar level by use of guards,
because it interferes with brace-based error recvoery.
Differential Revision: https://reviews.llvm.org/D127400