Fix istio proxy build after moving Envoy to hermteic toolchain

[krinkinmu]

What this PR does / why we need it:

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #

Special notes for your reviewer:

[istio-testing]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

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[krinkinmu]

/test all

[howardjohn]

Does this mean you can finally just run bazel build and it works??? amazing!!

[krinkinmu]

Does this mean you can finally just run bazel build and it works??? amazing!!

Almost, but there are corner cases. E.g., llvm tools themselves are not built statically, so they still depend on some external libraries, but at the very least installing clang should not be necessary.

And we still need to figure out if we want to go this way or rely on a local toolchain.

[zirain]

can you change this to --config=clang and give another try?

[krinkinmu]

I tested locally and it works, now will try on CI.

[zirain]

/test all