Attempt to make FreeBSD buildbot green.
Attempt to make FreeBSD buildbot green.

It seems that __cxa_demangle function on the buildbot tried to demangle
a variable "tlsvar" as a C++ symbol. Do not call that function unless
it does not start with "_Z" which is the prefix of mangled names.

git-svn-id: f6089bf0e6284f307027cef4f64114ee9ebb0424@257661 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lld,llvm-mirror/lld