Vec growth glue not treated as user-level when it could be.

[froystig]

We currently emit vec growth glue, but it is called using the push/pop mechanism (e.g. of trans_call_glue). In reality, the only call site for this glue is generated when translating vec append statements, so it really is user-level glue and need not adhere to the "worst-case glue-call args" max argument count. The fact that we don't do this costs us one extra word of worst-case glue-call args at the moment (7 words instead of the 6 we'd need otherwise).

This is a relatively minor issue, but now noted.

[graydon]

WONTFIX (not required for bootstrapping)