Fix IRBuilder on local operations outside of a function context

[kripken]

IRBuilder needs to check for a function context before doing
func->getLocalType(). Without such a check, a bad binary with a local
operation in say a global init would lead to a crash.

We don't actually need this for local.set, unlike tee and get, since
it doesn't call getLocalType, but this PR adds that too for consistency
of errors.

No other operations in IRBuilder were missing this check aside from
local operations.

Fixes #7178