add a new pop_back_val method which returns the value popped. This is

heretical from a STL standpoint, but is oh-so-useful for things that 
can't throw exceptions when copied, like, well, everything in LLVM.

llvm-svn: 60587

llvm/include/llvm/ADT/SmallVector.h

@@ -162,6 +162,12 @@ public:
     End->~T();
   }
   
+  T pop_back_val() {
+    T Result = back();
+    pop_back();
+    return Result;
+  }
+  
   void clear() {
     destroy_range(Begin, End);
     End = Begin;