[Bazel] Fix llvm-exegesis build post 12b0ab2c

12b0ab2c switched llvm-exegesis from using MCJIT to OrcJIT, which is a
different dep/library. This was ported over in the CMake build, but not
in the bazel build. This patch adjusts the llvm-exegesis deps in the
Bazel build to account for this change.