Use correct clang flag for size optimization (IDFGH-11295)

[storoj]

See https://clang.llvm.org/docs/CommandGuide/clang.html:

Code Generation Options
   -Oz Like -Os (and thus -O2), but reduces code size further.

Without -Oz enabled clang produced binaries that were too large.

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Generated by 🚫 dangerJS against 4acefd9

[ESP-Marius]

After looking into this, changing to -Oz does indeed seem reasonable. We;ll discuss it further internally.

Thanks for your contribution!

[ESP-Marius]

sha=4acefd9df00aff1d926937840d327c890df1803a

[SoucheSouche]

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