Fix stack-use-after-scope in CheckExplicitlyDefaultedMemberExceptionSpec

Summary:
Similar to r288685.
getExceptionSpec returned structure with pointers to temporarily object created
by computeImplicitExceptionSpec.

Reviewers: rsmith

Subscribers: aizatsky, cfe-commits

Differential Revision: https://reviews.llvm.org/D27422

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@288689 91177308-0d34-0410-b5e6-96231b3b80d8

Author: vitalybuka

lib/Sema/SemaDeclCXX.cpp

@@ -6299,8 +6299,8 @@ void Sema::CheckExplicitlyDefaultedMemberExceptionSpec(
   CallingConv CC = Context.getDefaultCallingConvention(/*IsVariadic=*/false,
                                                        /*IsCXXMethod=*/true);
   FunctionProtoType::ExtProtoInfo EPI(CC);
-  EPI.ExceptionSpec = computeImplicitExceptionSpec(*this, MD->getLocation(), MD)
-                          .getExceptionSpec();
+  auto IES = computeImplicitExceptionSpec(*this, MD->getLocation(), MD);
+  EPI.ExceptionSpec = IES.getExceptionSpec();
   const FunctionProtoType *ImplicitType = cast<FunctionProtoType>(
     Context.getFunctionType(Context.VoidTy, None, EPI));