[CMAKE] Fix Linux64 toolchain name
The toolchain is named with an extra -pc in its name (just like the 32
bits version) but it should not.
Using this mistaken name as the depends name will still work when the
host is a 64 bits linux as it will default to the good system.
cd depends make build-linux64 mkdir ../buildcmake && cd ../buildcmake cmake -GNinja .. \ -DCMAKE_TOOLCHAIN_FILE=../cmake/platforms/Linux64.cmake ninja
Reviewers: #bitcoin_abc, deadalnix
Reviewed By: #bitcoin_abc, deadalnix
Differential Revision: https://reviews.bitcoinabc.org/D4038