constexpr: Implement DR1358: An instantiation of a constexpr function which
can't produce a constant expression is not ill-formed (so long as some
instantiation of that function can produce a constant expression).

llvm-svn: 149802
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 6b92b0a..172e931 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -7302,7 +7302,7 @@
     }
 
     if (FD && FD->isConstexpr() && !FD->isInvalidDecl() &&
-        !CheckConstexprFunctionBody(FD, Body))
+        !CheckConstexprFunctionBody(FD, Body, IsInstantiation))
       FD->setInvalidDecl();
 
     assert(ExprCleanupObjects.empty() && "Leftover temporaries in function");