cmd/compile: make a type-specialized copy of encoding/binary.ReadUvarint
cmd/compile: make a type-specialized copy of encoding/binary.ReadUvarint

This is to get better escape analysis for a frequently-allocated object.

Change-Id: I1942a4e1c3cd1f0fa870bc8433a0165c18ce9c75
Reviewed-on: https://go-review.googlesource.com/c/go/+/435336
Reviewed-by: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@google.com>
Run-TryBot: David Chase <ae171625adc8645b8b79b7e405a6da5aba5341e0@google.com>
Reviewed-by: Matthew Dempsky <e56ac2c500064424afac424d4b5e53bd0570a731@google.com>

golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go