Preserve exception specs in function decl merging.

Exception specs are not part of the canonical type, but we shouldn't
drop them just because we merged a noreturn attribute.

Fixes PR17110.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190206 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 68df00d..34f7c46 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -2382,9 +2382,11 @@
   }
   
   if (RequiresAdjustment) {
-    NewType = Context.adjustFunctionType(NewType, NewTypeInfo);
-    New->setType(QualType(NewType, 0));
+    const FunctionType *AdjustedType = New->getType()->getAs<FunctionType>();
+    AdjustedType = Context.adjustFunctionType(AdjustedType, NewTypeInfo);
+    New->setType(QualType(AdjustedType, 0));
     NewQType = Context.getCanonicalType(New->getType());
+    NewType = cast<FunctionType>(NewQType);
   }
 
   // If this redeclaration makes the function inline, we may need to add it to