Output: Fix assertion failure on translation-unit-level operators

Refactoring in commit 917c646e (Output: Generalize exclusion of internal
`__castxml` builtins, 2016-04-18) introduced an unconditional call to
`clang::NamedDecl::getName`, but that method asserts that the name is
a valid identifier.  Instead call `getIdentifier` ourselves and check
the name only if it is a valid identifier.

GitHub-Issue: #62

1 files changed, 2 insertions, 0 deletions

diff --git a/test/input/nostart.cxx b/test/input/nostart.cxx
new file mode 100644
index 0000000..37374bc
--- /dev/null
+++ b/test/input/nostart.cxx
@@ -0,0 +1,2 @@
+class A;
+A operator+(A,A);