Work around missing handling of temporaries bound to default arguments.

Yet more problems due to the missing CXXBindTemporaryExpr in the CFG for
default arguments.

Unfortunately we cannot just switch off inserting temporaries for the
corresponding default arguments, as that breaks existing tests
(test/SemaCXX/return-noreturn.cpp:245).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@215554 91177308-0d34-0410-b5e6-96231b3b80d8