Driver-side concatenation flattens module names, but enum member
lookup keyed off the exact lhs ident — so `whence.CUR` worked while
`os.whence.CUR` fell through to w6l with `undefined main.whence`.
C side: fold TY_ENUM members in the post-cexpr cascade too, not
just the early SK_TYPE shortcut. The recursive cexpr lands the
inner N_DOT(os, whence) on the named enum type; the outer access
then folds normally.
Selfhost: cgdot now treats `N_IDENT.MEMBER` and `N_DOT.MEMBER` the
same way, keying off the leaf name. enumlookup strips a trailing
`.`-prefix from the lookup key.
Adds e2e test 700: `use os; os.whence.CUR as i32 == 1`.
Hojun-Cho
5149d10618