Auto merge of #23583 - servo:jdm-patch-56, r=SimonSapin
Auto merge of #23583 - servo:jdm-patch-56, r=SimonSapin

Force clang use on all platforms.

gcc builds are unlinkable on Linux at the moment. Let's standardize on clang.

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notriddle/servo,larsbergstrom/servo,saneyuki/servo,saneyuki/servo,KiChjang/servo,nnethercote/servo,splav/servo,KiChjang/servo,larsbergstrom/servo,saneyuki/servo,KiChjang/servo,DominoTree/servo,notriddle/servo,saneyuki/servo,KiChjang/servo,notriddle/servo,splav/servo,DominoTree/servo,larsbergstrom/servo,paulrouget/servo,nnethercote/servo,DominoTree/servo,nnethercote/servo,splav/servo,saneyuki/servo,nnethercote/servo,notriddle/servo,notriddle/servo,KiChjang/servo,nnethercote/servo,larsbergstrom/servo,notriddle/servo,larsbergstrom/servo,splav/servo,nnethercote/servo,notriddle/servo,notriddle/servo,splav/servo,saneyuki/servo,paulrouget/servo,paulrouget/servo,paulrouget/servo,DominoTree/servo,paulrouget/servo,splav/servo,paulrouget/servo,paulrouget/servo,DominoTree/servo,paulrouget/servo,splav/servo,DominoTree/servo,larsbergstrom/servo,KiChjang/servo,DominoTree/servo,larsbergstrom/servo,DominoTree/servo,nnethercote/servo,splav/servo,KiChjang/servo,DominoTree/servo,larsbergstrom/servo,paulrouget/servo,larsbergstrom/servo,notriddle/servo,larsbergstrom/servo,KiChjang/servo,saneyuki/servo,saneyuki/servo,KiChjang/servo,saneyuki/servo,DominoTree/servo,nnethercote/servo,nnethercote/servo,KiChjang/servo,splav/servo,paulrouget/servo,splav/servo,nnethercote/servo,saneyuki/servo,notriddle/servo