libstdc++: [_GLIBCXX_INLINE_VERSION] Add emul TLS symbols

libstdc++-v3/ChangeLog:

	* config/abi/pre/gnu-versioned-namespace.ver: Add missing emul TLS
	symbols.

libstdc++-v3/config/abi/pre/gnu-versioned-namespace.ver

@@ -78,6 +78,8 @@ GLIBCXX_8.0 {
 
     # thread/mutex/condition_variable/future
     __once_proxy;
+    __emutls_v._ZSt3__811__once_call;
+    __emutls_v._ZSt3__815__once_callable;
 
     # std::__convert_to_v
     _ZNSt3__814__convert_to_v*;