PR libstdc++/86655 - std::assoc_legendre should not constrain

2019-03-06  Edward Smith-Rowland  <3dw4rd@verizon.net>

	PR libstdc++/86655 - std::assoc_legendre should not constrain
	the value of m (or x).
	* include/tr1/legendre_function.tcc (__assoc_legendre_p,
	__sph_legendre): If degree > order Don't throw, return 0.
	(__legendre_p, __assoc_legendre_p): Don't constrain x either.
	* testsuite/special_functions/02_assoc_legendre/pr86655.cc: New test.
	* testsuite/special_functions/20_sph_legendre/pr86655.cc: New test.
	* testsuite/tr1/5_numerical_facilities/special_functions/
	02_assoc_legendre/pr86655.cc: New test.
	* testsuite/tr1/5_numerical_facilities/special_functions/
	22_sph_legendre/pr86655.cc: New test.

From-SVN: r269423