Preliminary work on support for 128bits integers

* fe.h, opt.ads (Enable_128bit_Types): New.
	* stand.ads (Standard_Long_Long_Long_Integer,
	S_Long_Long_Long_Integer): New.

gcc/ada/fe.h

@@ -192,6 +192,7 @@ extern Boolean In_Extended_Main_Code_Unit	(Entity_Id);
 #define Ada_Version			opt__ada_version
 #define Back_End_Inlining		opt__back_end_inlining
 #define Debug_Generated_Code		opt__debug_generated_code
+#define Enable_128bit_Types		opt__enable_128bit_types
 #define Exception_Extra_Info		opt__exception_extra_info
 #define Exception_Locations_Suppressed	opt__exception_locations_suppressed
 #define Exception_Mechanism		opt__exception_mechanism

gcc/ada/opt.ads

@@ -525,6 +525,13 @@ package Opt is
    --  dataflow analysis, which is not available. This behavior parallels that
    --  of the old ABE mechanism.
 
+   Enable_128bit_Types : Boolean := False;
+   --  GNAT
+   --  Set to True to enable the support for 128-bit types in the compiler.
+   --  The prerequisite is a 64-bit target that supports 128-bit computation.
+
+   --  WARNING: There is a matching C declaration of this variable in fe.h
+
    Error_Msg_Line_Length : Nat := 0;
    --  GNAT
    --  Records the error message line length limit. If this is set to zero,

gcc/ada/stand.ads

@@ -61,6 +61,7 @@ package Stand is
       S_Integer,
       S_Long_Integer,
       S_Long_Long_Integer,
+      S_Long_Long_Long_Integer,
 
       S_Natural,
       S_Positive,
@@ -283,6 +284,9 @@ package Stand is
    Standard_Long_Integer        : Entity_Id renames SE (S_Long_Integer);
    Standard_Long_Long_Integer   : Entity_Id renames SE (S_Long_Long_Integer);
 
+   Standard_Long_Long_Long_Integer : Entity_Id renames
+                                                 SE (S_Long_Long_Long_Integer);
+
    Standard_Op_Add              : Entity_Id renames SE (S_Op_Add);
    Standard_Op_And              : Entity_Id renames SE (S_Op_And);
    Standard_Op_Concat           : Entity_Id renames SE (S_Op_Concat);