cmd/go: line directives allows arbitrary execution during build (CVE-2023-39323)

[eks-distro-pr-bot]

"//line" directives can be used to bypass the restrictions on "//go:cgo_"
directives, allowing blocked linker and compiler flags to be passed during
compilation. This can result in unexpected execution of arbitrary code when
running "go build". The line directive requires the absolute path of the file in
which the directive lives, which makes exploting this issue significantly more
complex.

This is CVE-2023-39323 and Go issue https://go.dev/issue/63211.

---

This is a PRIVATE issue for CVE-2023-39323, tracked in http://b/296358534 and fixed by http://tg/2032884.

/cc @golang/security and @golang/release

[rcrozean]

#1182

[rcrozean]

Backported to 1.19.13 in #1192