cmd/compile: rename issafepoint -> hasStackMap
cmd/compile: rename issafepoint -> hasStackMap

Currently, this function conflates two (easily conflated!) concepts:
whether a Value is a safe-point and whether it has a stack map. In
particular, call Values may not be a safe-point, but may need a stack
map anyway in case the called function grows the stack.

Hence, rename this function to "hasStackMap", since that's really what
it represents.

For #36365.

Change-Id: I89839de0be8db3be3f0d3a7fb5fcf0b0b6ebc98a
Reviewed-on: https://go-review.googlesource.com/c/go/+/230540
Run-TryBot: Austin Clements <7ea35d812706d9213868749011af1ed4fa2f6aa0@google.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Cherry Zhang <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>

CAFxX/go,nawawi/go,akutz/go,akutz/go,golang/go,CAFxX/go,akutz/go,CAFxX/go,CAFxX/go,golang/go,nawawi/go,CAFxX/go,CAFxX/go,golang/go,nawawi/go,cloudflare/go,cloudflare/go,akutz/go,akutz/go,golang/go,akutz/go,akutz/go,cloudflare/go,nawawi/go,nawawi/go,nawawi/go,CAFxX/go,golang/go,golang/go,cloudflare/go,cloudflare/go,akutz/go,nawawi/go,golang/go,cloudflare/go,CAFxX/go,nawawi/go,cloudflare/go,golang/go,cloudflare/go