Revert^2: dexopt: Fix target-sdk-version argument creation

Refactor CL I8fdf96cfe0343042d1a868ca09e6c6b9a629b967 has a typo
which leaves the target-sdk-version argument of dex2oat always empty.
Fix the issue.

This reverts commit 142836515437bec4545d982387895190b8e5c678.

Test: manual inspection of command line arguments
Test: adb shell pm compile -m speed <package>
Change-Id: I6b92e8c595e3c00d71ab13d976ee43f58d1a0013
diff --git a/cmds/installd/dexopt.cpp b/cmds/installd/dexopt.cpp
index 3d7feb7..acc0647 100644
--- a/cmds/installd/dexopt.cpp
+++ b/cmds/installd/dexopt.cpp
@@ -368,7 +368,7 @@
         std::string dex2oat_image_fd;
         std::string target_sdk_version_arg;
         if (target_sdk_version != 0) {
-            StringPrintf("-Xtarget-sdk-version:%d", target_sdk_version);
+            target_sdk_version_arg = StringPrintf("-Xtarget-sdk-version:%d", target_sdk_version);
         }
         std::string class_loader_context_arg;
         if (class_loader_context != nullptr) {
@@ -471,7 +471,7 @@
         if (disable_cdex) {
             AddArg(kDisableCompactDexFlag);
         }
-        AddArg(target_sdk_version_arg);
+        AddRuntimeArg(target_sdk_version_arg);
         if (enable_hidden_api_checks) {
             AddRuntimeArg("-Xhidden-api-checks");
         }