[master] update to go1.21.4

[thaJeztah]

go1.21.4 (released 2023-11-07) includes security fixes to the path/filepath package, as well as bug fixes to the linker, the runtime, the compiler, and the go/types, net/http, and runtime/cgo packages. See the Go 1.21.4 milestone on our issue tracker for details:

• https://github.com/golang/go/issues?q=milestone%3AGo1.21.4+label%3ACherryPickApproved
• full diff: golang/go@go1.21.3...go1.21.4

from the security mailing:

[security] Go 1.21.4 and Go 1.20.11 are released

Hello gophers,

We have just released Go versions 1.21.4 and 1.20.11, minor point releases.

These minor releases include 2 security fixes following the security policy:

• path/filepath: recognize \??\ as a Root Local Device path prefix.

  On Windows, a path beginning with \??\ is a Root Local Device path equivalent
  to a path beginning with \\?\. Paths with a \??\ prefix may be used to
  access arbitrary locations on the system. For example, the path \??\c:\x
  is equivalent to the more common path c:\x.

  The filepath package did not recognize paths with a \??\ prefix as special.

  Clean could convert a rooted path such as \a\..\??\b into
  the root local device path \??\b. It will now convert this
  path into .\??\b.

  IsAbs did not report paths beginning with \??\ as absolute.
  It now does so.

  VolumeName now reports the \??\ prefix as a volume name.

  Join(`, ??, b)could convert a seemingly innocent sequence of path elements into the root local device path??\b. It will now convert this to .??\b`.

  This is CVE-2023-45283 and https://go.dev/issue/63713.

• path/filepath: recognize device names with trailing spaces and superscripts

  The IsLocal function did not correctly detect reserved names in some cases:

  • reserved names followed by spaces, such as "COM1 ".
  • "COM" or "LPT" followed by a superscript 1, 2, or 3.

  IsLocal now correctly reports these names as non-local.

  This is CVE-2023-45284 and https://go.dev/issue/63713.