os: use GetTempPath2 on Windows if available
This generates GetTempPath2. Go now tries to determine if the windows it runs on has GetTempPath2 by finding it only once at the loading time. If GetTempPath2 exists, it sets the flag so that any calls to tempDir will use it. If it doesn't exist, Go then uses GetTempPath.
GetTempPath2 was generated into internal/syscall/windows since syscall is locked down.
Fixes #56899
Change-Id: Iff08502aebc787fde802ee9496c070c982fbdc08
GitHub-Last-Rev:
b77938953404b4e8e11f829c742e3eb109580c5e
GitHub-Pull-Request: golang/go#57980
Reviewed-on: https://go-review.googlesource.com/c/go/+/463219
Run-TryBot: Quim Muntal <quimmuntal@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Quim Muntal <quimmuntal@gmail.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>