ada: Rename Is_Infinity to Is_Infinity_Or_NaN in System.Double_Real

ada: Rename Is_Infinity to Is_Infinity_Or_NaN in System.Double_Real

The predicate is used to detect corner cases in multiplicative operations
and also returns True for NaNs.

gcc/ada/ChangeLog:

	* libgnat/s-dourea.adb (Is_Infinity): Rename to...
	(Is_Infinity_Or_NaN): ...this.
	("*"): Adjust accordingly.
	("/"): Likewise.
	(Sqr): Likewise.
	* libgnat/s-dorepr.adb (Two_Prod): Likewise.
	(Two_Sqr): Likewise.
	* libgnat/s-dorepr__fma.adb (Two_Prod): Likewise.