PR libstdc++/82644 define TR1 hypergeometric functions in strict modes

PR libstdc++/82644 define TR1 hypergeometric functions in strict modes

Following a recent change for PR 82644 the non-standard hypergeomtric
functions are not defined by <cmath> when __STRICT_ANSI__ is defined
(e.g. for -std=c++17, or -std=c++14 -D__STDCPP_WANT_MATH_SPEC_FUNCS__).
That caused errors in <tr1/cmath> because the using-declarations for
tr1::hyperg et al are invalid in strict modes.

The solution is to define the TR1 hypergeometric functions inline in
<tr1/cmath> if __STRICT_ANSI__ is defined.

	PR libstdc++/82644
	* include/tr1/cmath [__STRICT_ANSI__] (hypergf, hypergl, hyperg): Use
	inline definitions instead of using-declarations.
	[__STRICT_ANSI__] (conf_hypergf, conf_hypergl, conf_hyperg): Likewise.
	* testsuite/tr1/5_numerical_facilities/special_functions/
	07_conf_hyperg/compile_cxx17.cc: New.
	* testsuite/tr1/5_numerical_facilities/special_functions/
	17_hyperg/compile_cxx17.cc: New.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@259912 138bc75d-0d04-0410-961f-82ee72b054a4