Update SetVector to rely on the underlying set's insert to return a pair<iterator, bool>

This is to be consistent with StringSet and ultimately with the standard
library's associative container insert function.

This lead to updating SmallSet::insert to return pair<iterator, bool>,
and then to update SmallPtrSet::insert to return pair<iterator, bool>,
and then to update all the existing users of those functions...

llvm-svn: 222334
diff --git a/llvm/lib/AsmParser/LLParser.cpp b/llvm/lib/AsmParser/LLParser.cpp
index b7818bb..2c835f9 100644
--- a/llvm/lib/AsmParser/LLParser.cpp
+++ b/llvm/lib/AsmParser/LLParser.cpp
@@ -3735,7 +3735,7 @@
         ParseTypeAndBasicBlock(DestBB, PFS))
       return true;
 
-    if (!SeenCases.insert(Constant))
+    if (!SeenCases.insert(Constant).second)
       return Error(CondLoc, "duplicate case value in switch");
     if (!isa<ConstantInt>(Constant))
       return Error(CondLoc, "case value is not a constant integer");