cmd/compile: make funccompile non-reentrant

Currently, there's awkward reentrancy issue with funccompile:

    funccompile -> compile -> dtypesym -> geneq/genhash/genwrapper -> funccompile

Though it's not a problem at this moment, some attempts by @mdempsky to
move order/walk/instrument into buildssa was failed, due to SSA cache
corruption.

This commit fixes that reentrancy issue, by making generated functions
to be pumped through the same compile workqueue that normal functions
are compiled. We do this by adding them to xtop, instead of calling
funccompile directly in geneq/genhash/genwrapper. In dumpdata, we look
for uncompiled functions in xtop instead of compilequeue, then finish
compiling them.

Updates #38463
Fixes #33485

Change-Id: Ic9f0ce45b56ae2ff3862f17fd979253ddc144bb5
Reviewed-on: https://go-review.googlesource.com/c/go/+/254617


Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Keith Randall <khr@golang.org>
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>