Remove cross-compilation & use native runners with different architectures

Currently, the arm64 linux jobs are failing because they need to execute `llvm-config`. The runner is x86 while we are cross-compiling to arm64, so the process fails to run. 

Github has runners on both x86 and arm64 architectures, so we could just use that instead of cross-compiling. Then we could directly call `llvm-config` inside the runner.