[Driver] Follow-up to r211598, r211663. Do not build a dynamic linker
path using sub-strings concatenation. Return the whole string explicitly.

llvm-svn: 211665
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index 4ccb863..48528d9 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -6929,8 +6929,8 @@
     CmdArgs.push_back("-ldl");
 }
 
-static Twine getLinuxDynamicLinker(const ArgList &Args,
-                                   const toolchains::Linux &ToolChain) {
+static StringRef getLinuxDynamicLinker(const ArgList &Args,
+                                       const toolchains::Linux &ToolChain) {
   if (ToolChain.getTriple().getEnvironment() == llvm::Triple::Android) {
     if (ToolChain.getTriple().isArch64Bit())
       return "/system/bin/linker64";
@@ -6964,11 +6964,11 @@
     return "/lib/ld.so.1";
   } else if (ToolChain.getArch() == llvm::Triple::mips64 ||
              ToolChain.getArch() == llvm::Triple::mips64el) {
-    Twine LinkerFile =
-        mips::isNaN2008(Args) ? "ld-linux-mipsn8.so.1" : "ld.so.1";
     if (mips::hasMipsAbiArg(Args, "n32"))
-      return "/lib32/" + LinkerFile;
-    return "/lib64/" + LinkerFile;
+      return mips::isNaN2008(Args) ? "/lib32/ld-linux-mipsn8.so.1"
+                                   : "/lib32/ld.so.1";
+    return mips::isNaN2008(Args) ? "/lib64/ld-linux-mipsn8.so.1"
+                                 : "/lib64/ld.so.1";
   } else if (ToolChain.getArch() == llvm::Triple::ppc)
     return "/lib/ld.so.1";
   else if (ToolChain.getArch() == llvm::Triple::ppc64 ||