build: avoid embedding depends paths in build RPATH #36053

After PR #33247 removed CMAKE_SKIP_BUILD_RPATH from the CMake build system as part of changes related to Guix binary checks, Linux builds using the depends toolchain could embed the absolute depends/<host>/lib path in build-tree binaries.

One user-visible consequence was incorrect font rendering in the Bitcoin Core Qt GUI. Instead of rendering the bundled RobotoMono-Bold.ttf font as intended, the GUI could fall back to a system-provided font and sizing, resulting in text that was unpleasant to read and, in some cases, difficult to read.

This PR restores build-RPATH suppression specifically for the depends toolchain, without reverting the broader changes from #33247 or affecting Guix builds. It also prevents Linux binaries built with depends from containing the absolute depends library path in their RPATH/RUNPATH.

Tested on Linux x86_64 with depends builds on v31.1 and current master. After this change, bitcoin-qt, bitcoin-gui, and test_bitcoin-qt contain no RPATH/RUNPATH, and their generated link commands contain no -Wl,-rpath.

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For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/36053.

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