Reland "SuperSize: Remove --tool-prefix"

This reverts commit af4d664e.

Reason for reland: updated diagnose_bloat.py in separate change
(https://crrev.com/c/3395397).

Original change's description:
> Revert "SuperSize: Remove --tool-prefix"
>
> This reverts commit 0340b93d.
>
> Reason for revert: Broke diagnose_bloat.py
>
> Original change's description:
> > SuperSize: Remove --tool-prefix
> >
> > The idea that toolchains are interchangeable didn't really turn out to
> > be true. SuperSize always works better with LLVM tools, with the
> > exception of disassembling, and it simplifies the code to not pass
> > around tool_prefix.
> >
> > The tool_prefix can still be overridden in tests via the environment
> > variable: SUPERSIZE_TOOL_PREFIX
> >
> > Bug: None
> > Change-Id: I169a4fff7221e25c72a548109739387771d8c41a
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3383921


> > Reviewed-by: Samuel Huang <huangs@chromium.org>
> > Commit-Queue: Andrew Grieve <agrieve@chromium.org>
> > Cr-Commit-Position: refs/heads/main@{#959303}
>
> Bug: None
> Change-Id: I807e791352de473bcad695ddc60761c38f4905c8
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3390031
> Auto-Submit: Andrew Grieve <agrieve@chromium.org>
> Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Cr-Commit-Position: refs/heads/main@{#959486}

Bug: None
Change-Id: I1ac663ff9470cbb20dae9b80d08e46e02ff59eb8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3390032


Reviewed-by: Samuel Huang <huangs@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/main@{#960147}