Fix make build-binaries

[zmb3]

The dockerized build (make -C build.assets build-binaries) fails with GLIBC errors because it is a multi-stage build that runs across several different containers.

First, we build the webassets in buildbox-node. Then we build the Teleport binaries in buildbox-centos7, reusing the webassets built previously.

The issue arises because buildbox-node runs a newer version of GLIBC than buildbox-centos7, and we weren't properly cleaning some build artifacts when switching from one builder to another. As a result, the centos7 builder would see intermediate artifacts with a dependency on a GLIBC version that is too new.

Fix the issue by ensuring we run a clean-build after hopping into the centos7 container.

Closes #62594

[hugoShaka]

I ran it from my macbook and it worked. I don't have an amd laptop to test this on today. I can spin up a new VM and do the test if needed.

The logs are full of scary things, I don't know if we want to fix those:

make[2]: Entering directory '/go/src/github.com/gravitational/teleport'
go: errors parsing go.mod:
/go/src/github.com/gravitational/teleport/go.mod:3: invalid go version '1.25.5': must match format 1.23
/go/src/github.com/gravitational/teleport/go.mod:5: unknown block type: ignore
/go/src/github.com/gravitational/teleport/go.mod:663: unknown block type: tool
go: errors parsing go.mod:
/go/src/github.com/gravitational/teleport/go.mod:3: invalid go version '1.25.5': must match format 1.23
/go/src/github.com/gravitational/teleport/go.mod:5: unknown block type: ignore
/go/src/github.com/gravitational/teleport/go.mod:663: unknown block type: tool
go: errors parsing go.mod:
/go/src/github.com/gravitational/teleport/go.mod:3: invalid go version '1.25.5': must match format 1.23
/go/src/github.com/gravitational/teleport/go.mod:5: unknown block type: ignore
/go/src/github.com/gravitational/teleport/go.mod:663: unknown block type: tool

[zmb3]

The logs are full of scary things, I don't know if we want to fix those

Not right now, but I can explain why you see those.

The makefile invokes go a bunch of times when evaluating variables, even if the target we call doesn't end up needing go.

(We've made some improvements here in the past - see #9776 and #25870, but the behavior persists).

The buildbox-node is based on Debian Buster, and we don't explicitly install Go there because we don't actually need it - we only use that container to build the web assets. As a result, the makefile ends up invoking the system Go, and Buster still ships with a very old version (something like 1.13) in its packages. This old version of Go chokes on some of the newer directives in our go.mod.

[backport-bot-workflows]

@zmb3 See the table below for backport results.

Branch	Result
branch/v18	Failed