PR libstdc++/83140 - assoc_legendre returns negated value when m is odd

PR libstdc++/83140 - assoc_legendre returns negated value when m is odd

2018-05-10  Edward Smith-Rowland  <3dw4rd@verizon.net>

	PR libstdc++/83140 - assoc_legendre returns negated value when m is odd
	* include/tr1/legendre_function.tcc (__assoc_legendre_p): Add __phase
	argument defaulted to +1.  Doxy comments on same.
	* testsuite/special_functions/02_assoc_legendre/
	check_assoc_legendre.cc: Regen.
	* testsuite/tr1/5_numerical_facilities/special_functions/
	02_assoc_legendre/check_tr1_assoc_legendre.cc: Regen.

From-SVN: r260115