Replace a hand rolled loop with a lovely StringRef helper we have these
days. No functionality changed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151048 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/Triple.cpp b/lib/Support/Triple.cpp
index 11cbb5f..72f3131 100644
--- a/lib/Support/Triple.cpp
+++ b/lib/Support/Triple.cpp
@@ -335,10 +335,7 @@
 std::string Triple::normalize(StringRef Str) {
   // Parse into components.
   SmallVector<StringRef, 4> Components;
-  for (size_t First = 0, Last = 0; Last != StringRef::npos; First = Last + 1) {
-    Last = Str.find('-', First);
-    Components.push_back(Str.slice(First, Last));
-  }
+  Str.split(Components, "-");
 
   // If the first component corresponds to a known architecture, preferentially
   // use it for the architecture.  If the second component corresponds to a