allows a typedefed named to immediately follow its typedef

[ivg]

In the following example

typedef int T; T foo(void);

i.e., when the next token after a typedef is the typedefed name, the T
token is already looked ahead, so it is recognized as IDENT not as
NAMED_TYPE, e.g., here is the trace,

Lookahead token is now IDENT (15-16) <-- 'T'
Reducing production typedef -> TYPEDEF typedef_type typedef_defs SEMICOLON
adding T <-- debug output from the lexer, indicating that T was added

The solution is to factor out the typedef non-terminal and move the
semicolon to globals so that we have it reduced earlier, when the next
token is SEMICOLON:

Reducing production typedef -> TYPEDEF typedef_type typedef_defs
adding T <-- typedef reduces before semicolon
State 542:
Shifting (SEMICOLON) to state 543
State 543:
Lookahead token is now NAMED_TYPE (15-16) <-- it is now recognized as type name

Fixes #23