Drop useless const in for-range loops.

StringRefs always point to immutable memory so the const doesn't add value
here. Also quiets clang's -Wrange-loop-analysis which warns about the implicit
copying.

llvm-svn: 248496
diff --git a/clang/lib/Driver/ToolChains.cpp b/clang/lib/Driver/ToolChains.cpp
index 04ea874..668fc02 100644
--- a/clang/lib/Driver/ToolChains.cpp
+++ b/clang/lib/Driver/ToolChains.cpp
@@ -1213,20 +1213,20 @@
   for (const std::string &Prefix : Prefixes) {
     if (!llvm::sys::fs::exists(Prefix))
       continue;
-    for (const StringRef Suffix : CandidateLibDirs) {
+    for (StringRef Suffix : CandidateLibDirs) {
       const std::string LibDir = Prefix + Suffix.str();
       if (!llvm::sys::fs::exists(LibDir))
         continue;
-      for (const StringRef Candidate : ExtraTripleAliases) // Try these first.
+      for (StringRef Candidate : ExtraTripleAliases) // Try these first.
         ScanLibDirForGCCTriple(TargetTriple, Args, LibDir, Candidate);
-      for (const StringRef Candidate : CandidateTripleAliases)
+      for (StringRef Candidate : CandidateTripleAliases)
         ScanLibDirForGCCTriple(TargetTriple, Args, LibDir, Candidate);
     }
-    for (const StringRef Suffix : CandidateBiarchLibDirs) {
+    for (StringRef Suffix : CandidateBiarchLibDirs) {
       const std::string LibDir = Prefix + Suffix.str();
       if (!llvm::sys::fs::exists(LibDir))
         continue;
-      for (const StringRef Candidate : CandidateBiarchTripleAliases)
+      for (StringRef Candidate : CandidateBiarchTripleAliases)
         ScanLibDirForGCCTriple(TargetTriple, Args, LibDir, Candidate,
                                /*NeedsBiarchSuffix=*/ true);
     }
@@ -3091,7 +3091,7 @@
     SmallVector<StringRef, 16> Lines;
     Data.split(Lines, "\n");
     Distro Version = UnknownDistro;
-    for (const StringRef Line : Lines)
+    for (StringRef Line : Lines)
       if (Version == UnknownDistro && Line.startswith("DISTRIB_CODENAME="))
         Version = llvm::StringSwitch<Distro>(Line.substr(17))
                       .Case("hardy", UbuntuHardy)