Convert StringMapEntry::Create to use StringRef instead of start/end pointers. Simpliies all in tree call sites. No functional change.

llvm-svn: 210638
diff --git a/llvm/lib/Support/StringPool.cpp b/llvm/lib/Support/StringPool.cpp
index ff607cf..76faabc 100644
--- a/llvm/lib/Support/StringPool.cpp
+++ b/llvm/lib/Support/StringPool.cpp
@@ -27,7 +27,7 @@
   if (I != InternTable.end())
     return PooledStringPtr(&*I);
   
-  entry_t *S = entry_t::Create(Key.begin(), Key.end());
+  entry_t *S = entry_t::Create(Key);
   S->getValue().Pool = this;
   InternTable.insert(S);