Fix performance-for-range-copy clang-tidy issues

Test: m tidy-art
Bug: 213953102
Change-Id: I206a44aa4c1f3f2f91e4f94831d042e903c71c65
diff --git a/compiler/utils/assembler_test_base.h b/compiler/utils/assembler_test_base.h
index bf73808..de19d66 100644
--- a/compiler/utils/assembler_test_base.h
+++ b/compiler/utils/assembler_test_base.h
@@ -59,7 +59,7 @@
 
   // This is intended to be run as a test.
   bool CheckTools() {
-    for (auto cmd : { GetAssemblerCommand()[0], GetDisassemblerCommand()[0] }) {
+    for (const std::string& cmd : { GetAssemblerCommand()[0], GetDisassemblerCommand()[0] }) {
       if (!OS::FileExists(cmd.c_str())) {
         LOG(ERROR) << "Could not find " << cmd;
         return false;