Fix printing native CPU on cross-compiled compiler.

Author: ehuss

compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp

@@ -310,12 +310,14 @@ static size_t getLongestEntryLength(ArrayRef<KV> Table) {
 extern "C" void LLVMRustPrintTargetCPUs(LLVMTargetMachineRef TM) {
   const TargetMachine *Target = unwrap(TM);
   const MCSubtargetInfo *MCInfo = Target->getMCSubtargetInfo();
-  const Triple::ArchType HostArch = Triple(sys::getProcessTriple()).getArch();
+  const Triple::ArchType HostArch = Triple(sys::getDefaultTargetTriple()).getArch();
   const Triple::ArchType TargetArch = Target->getTargetTriple().getArch();
   const ArrayRef<SubtargetSubTypeKV> CPUTable = MCInfo->getCPUTable();
   unsigned MaxCPULen = getLongestEntryLength(CPUTable);
 
   printf("Available CPUs for this target:\n");
+  // Don't print the "native" entry when the user specifies --target with a
+  // different arch since that could be wrong or misleading.
   if (HostArch == TargetArch) {
     const StringRef HostCPU = sys::getHostCPUName();
     printf("    %-*s - Select the CPU of the current host (currently %.*s).\n",