misc/cgo/test: add asan and msan arena tests

misc/cgo/test: add asan and msan arena tests

While we're here, replace a couple uses of os.Environ with cmd.Environ.

For #51317.

Change-Id: Ic5cf4a887a7975a8281223eec0f94df230b6f095
Reviewed-on: https://go-review.googlesource.com/c/go/+/431955
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>