gcc/c-family:

	PR c++/81852
	* c-cppbuiltin.c (c_cpp_builtins): Define __cpp_threadsafe_static_init.

gcc/testsuite:

	PR c++/81852
	* g++.dg/cpp1y/feat-cxx11.C: Check __cpp_threadsafe_static_init.
	* g++.dg/cpp1y/feat-cxx14.C: Likewise.
	* g++.dg/cpp1y/feat-cxx98.C: Likewise.
	* g++.dg/cpp1y/feat-neg.C: Likewise.
	* g++.dg/cpp1z/feat-cxx1z.C: Likewise.

From-SVN: r251939