* module/language/c99/compiler.mes (expr->accu, expr->accu*): fixes
for foo->bar[baz].
(expr->pointer): Support i-sel.
(p-expr->type): Support add, sub, de-ref, ref-to.
* scaffold/tests/7f-struct-pointer-arithmetic.c: Test it.
* make.scm (add-scaffold-test): Build it.