llvm BPF target: add missed source files

llvm BPF target: add missed source files

Otherwise, linking llvm binaries with this target enabled (which is not
the default) will fail with a number of undefined symbol errors:

  ld: error: undefined symbol: llvm::initializeBPFAdjustOptPass(llvm::PassRegistry&)
  ld: error: undefined symbol: llvm::initializeBPFCheckAndAdjustIRPass(llvm::PassRegistry&)
  ld: error: undefined symbol: llvm::createBPFCheckAndAdjustIR()
  ld: error: undefined symbol: llvm::createBPFAdjustOpt()
  ld: error: undefined symbol: llvm::BPFAdjustOptPass::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&)

Reported by:	Michael Dexter <editor@callfortesting.org>
MFC after:	3 days