the name and type of the object declared and construct a DECL node
for it.
- DECLSPECS is a chain of tree_list nodes whose value fields
- are the storage classes and type specifiers.
+ DECLSPECS points to the representation of declaration-specifier
+ sequence that precedes declarator.
DECL_CONTEXT says which syntactic context this declaration is in:
NORMAL for most contexts. Make a VAR_DECL or FUNCTION_DECL or TYPE_DECL.