ccache: create the compiler shims without sudo

[presto8]

'sudo ln -s' left ~/.local/bin/{gcc,g++,cc,c++} owned by root inside
the user's own home directory, so they could not be inspected or
cleaned up without escalating again. The directory is user-writable and
needs no privilege.

Replace 'sudo rm -f' + 'sudo ln -s' with a plain 'ln -sf' (which also
makes the function re-runnable), declare the loop variable local, and
use 'command -v' rather than the external 'which'.

Existing root-owned links are replaced on the next run, since removal
depends on write permission to the directory rather than file
ownership.

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🤖 Generated with Claude Code

[Copilot]

🟢 Approval recommended

The change is narrowly scoped, aligns with the PR rationale, and improves correctness by avoiding root-owned files in the user’s home directory.

Pull request overview

This PR updates the install_ccache portion of the setup script to create compiler shim symlinks in ~/.local/bin without using sudo, preventing root-owned symlinks inside a user’s home directory and making the operation safely re-runnable.

Changes:

• Replace sudo rm + sudo ln -s with ln -sf for idempotent symlink creation in a user-writable directory.
• Resolve the ccache executable path once via command -v and reuse it across the shim creation loop.
• Scope loop variables locally within install_ccache to avoid leaking shell variables.

File summaries

File	Description
setup	Removes unnecessary sudo from ccache compiler-shim symlink creation and makes the operation idempotent.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 0
• Review effort level: Lite

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