Restore the logging of compilation progress on target device.

Yesterday's removal of "fork" on the target compilation accidentally
dropped the logging. Restoring it back here.

Change-Id: I32c58ee85b81f443edd3313ccee3cf56227d5017
diff --git a/src/compiler_llvm/compilation_unit.cc b/src/compiler_llvm/compilation_unit.cc
index 10844b8..e433670 100644
--- a/src/compiler_llvm/compilation_unit.cc
+++ b/src/compiler_llvm/compilation_unit.cc
@@ -171,7 +171,9 @@
 
   if (thread_count == 1) {
     llvm::raw_string_ostream str_os(elf_image_);
-    return MaterializeToFile(str_os, insn_set_);
+    bool success = MaterializeToFile(str_os, insn_set_);
+    LOG(INFO) << "Compilation Unit: " << elf_idx_ << (success ? " (done)" : " (failed)");
+    return success;
   }
 
   // Prepare the pipe between parent process and child process