PR libstdc++/51333 Define recursive_init_error constructor non-inline

PR libstdc++/51333 Define recursive_init_error constructor non-inline

The recursive_init_error class is defined in a header, with an inline
constructor, but the definition of the vtable and destructor are not
exported from the shared library. With -fkeep-inline-functions the
constructor gets emitted in user code, and requires the (non-exported)
vtable. This fails to link.

As far as I can tell, the recursive_init_error class definition was
moved into <cxxabi.h> so it could be documented with Doxygen, not for
any technical reason. But now it's there (and documented), somebody
could be relying on it, by catching that type and possibly performing
derived-to-base conversions to the std::exception base class. So the
conservative fix is to leave the class definition in the header but make
the constructor non-inline. This still allows the type to be caught and
still defines its base class.

Backport from mainline
2019-07-29  Jonathan Wakely  <jwakely@redhat.com>

	PR libstdc++/51333
	* libsupc++/cxxabi.h (__gnu_cxx::recursive_init_error): Do not define
	constructor inline.
	* libsupc++/guard_error.cc (__gnu_cxx::recursive_init_error): Define
	constructor.
	* testsuite/18_support/51333.cc: New test.

From-SVN: r273946