[build] Prepare workerd for explicit libc++ linkage

[KirillTim]

Edgeworker now supplies libc++ globally through link_extra_libs rather
than toolchain linker flags. Fix the workerd targets that cannot use
this dependency directly.

Release note: None

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[codspeed-hq]

Merging this PR will not alter performance

✅ 72 untouched benchmarks
⏩ 129 skipped benchmarks¹

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_{Comparing ktimofeev/bazel-hiremtic-libcxx (fc09d08) with main (0cfe647)}

Footnotes

1. 129 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[npaun]

Seems reasonable - would like to discuss the overall motivation for this though.

[fhanau]

Seems reasonable - would like to discuss the overall motivation for this though.

Yeah I think this merits some more discussion before moving forward with this approach – this adds complexity for every binary that doesn't use libc++, we should only do this if there's no better alternative. In particular, I think we can use LD_LIBRARY_PATH to avoid needing this.