[Ada] Export Opt.Assume_No_Invalid_Values for use in back-end

gcc/ada/

	* fe.h (Assume_No_Invalid_Values): Declare.
	* opt.ads (Assume_No_Invalid_Values): Add warning comment.

gcc/ada/fe.h

@@ -190,6 +190,7 @@ extern Boolean In_Extended_Main_Code_Unit	(Entity_Id);
 /* opt: */
 
 #define Ada_Version			opt__ada_version
+#define Assume_No_Invalid_Values	opt__assume_no_invalid_values
 #define Back_End_Inlining		opt__back_end_inlining
 #define Debug_Generated_Code		opt__debug_generated_code
 #define Enable_128bit_Types		opt__enable_128bit_types
@@ -211,6 +212,7 @@ typedef enum {
 } Exception_Mechanism_Type;
 
 extern Ada_Version_Type Ada_Version;
+extern Boolean Assume_No_Invalid_Values;
 extern Boolean Back_End_Inlining;
 extern Boolean Debug_Generated_Code;
 extern Boolean Enable_128bit_Types;

gcc/ada/opt.ads

@@ -191,6 +191,8 @@ package Opt is
    --  are valid and in range of their representations. This feature is now
    --  fully enabled in the compiler.
 
+   --  WARNING: There is a matching C declaration of this variable in fe.h
+
    Back_Annotate_Rep_Info : Boolean := False;
    --  GNAT
    --  If set True, enables back annotation of representation information