* checks.adb:
        (Insert_Valid_Check): Avoid unnecessary generation of junk declaration
        when no invalid values exist, Avoid duplicate read of atomic variable.

        * cstand.adb (Build_Signed_Integer_Type): Set Is_Known_Valid
        (Standard_Unsigned): Set Is_Known_Valid

        * sem_ch3.adb (Analyze_Subtype_Declaration): Copy Is_Known_Valid on
	subtype declaration if no constraint.
        (Set_Modular_Size): Set Is_Known_Valid if appropriate
        (Build_Derived_Numeric_Type): Copy Is_Known_Valid if no constraint

From-SVN: r145836