Disable tests that only pass for GNU dialects

Disable tests that only pass for GNU dialects

The airy and hypergeometric functions are non-standard extensions and
are only defined for -std=gnu++NN dialects, not -std=c++NN ones.

	* ext/special_functions/airy_ai/check_nan.cc: Skip test for
	non-standard extension when a strict -std=c++NN dialect is used.
	* ext/special_functions/airy_ai/check_value.cc: Likewise.
	* ext/special_functions/airy_ai/compile.cc: Likewise.
	* ext/special_functions/airy_bi/check_nan.cc: Likewise.
	* ext/special_functions/airy_bi/check_value.cc: Likewise.
	* ext/special_functions/airy_bi/compile.cc: Likewise.
	* ext/special_functions/conf_hyperg/check_nan.cc: Likewise.
	* ext/special_functions/conf_hyperg/check_value.cc: Likewise.
	* ext/special_functions/conf_hyperg/compile.cc: Likewise.
	* ext/special_functions/hyperg/check_nan.cc: Likewise.
	* ext/special_functions/hyperg/check_value.cc: Likewise.
	* ext/special_functions/hyperg/compile.cc: Likewise.

From-SVN: r265330