Golang cmd/cgo/internal/swig,cmd/go,x/build: swig cgo tests incompatible with C++ toolchain on builders [1.21 backport]

@dmitshur requested issue #67698 to be considered for backport to the next 1.21 minor release.

@gopherbot Please consider this for backport, in particular ~CL 589295~ CL 589495 and CL 589296. They apply test-only fixes that are needed to fix builder failures in newly running tests after a builder change.

Comment From: gopherbot

Change https://go.dev/cl/591378 mentions this issue: [release-branch.go1.21] cmd/cgo/internal/testsanitizers: make the libfuzzer tests all short

Comment From: gopherbot

Change https://go.dev/cl/591377 mentions this issue: [release-branch.go1.21] cmd/cgo/internal/swig: force use of lld for LTO tests on the builders

Comment From: gopherbot

Closed by merging 537ec6f21ec4b69142b9c5c9f8bcb2c66cf68274 to release-branch.go1.21.