[Ada] Clean up in Interfaces.C.Extensions

gcc/ada/

	* libgnat/i-cexten.ads (long_long, unsigned_long_long): Now
	subtypes of Interfaces.C types.
	* libgnat/a-calcon.ads, libgnat/a-calcon.adb
	(To_Unix_Nano_Time): Use Interfaces.C.long_long instead of
	Interfaces.C.Extensions.long_long.

gcc/ada/libgnat/a-calcon.adb

@@ -30,7 +30,6 @@
 ------------------------------------------------------------------------------
 
 with Interfaces.C;            use Interfaces.C;
-with Interfaces.C.Extensions; use Interfaces.C.Extensions;
 
 package body Ada.Calendar.Conversions is
 

gcc/ada/libgnat/a-calcon.ads

@@ -33,7 +33,6 @@
 --  time models - Time, Duration, struct tm and struct timespec.
 
 with Interfaces.C;
-with Interfaces.C.Extensions;
 
 package Ada.Calendar.Conversions is
 
@@ -112,7 +111,7 @@ package Ada.Calendar.Conversions is
    --  fit into a Time value.
 
    function To_Unix_Nano_Time
-     (Ada_Time : Time) return Interfaces.C.Extensions.long_long;
+     (Ada_Time : Time) return Interfaces.C.long_long;
    --  Convert a time value represented as number of time units since the Ada
    --  implementation-defined Epoch to a value relative to the Unix Epoch. The
    --  units of the result are nanoseconds. Raises Time_Error if the result

gcc/ada/libgnat/i-cexten.ads

@@ -61,8 +61,8 @@ package Interfaces.C.Extensions is
 
    --  64-bit integer types
 
-   subtype long_long is Long_Long_Integer;
-   type unsigned_long_long is mod 2 ** 64;
+   subtype long_long is Interfaces.C.long_long;
+   subtype unsigned_long_long is Interfaces.C.unsigned_long_long;
 
    --  128-bit integer type available on 64-bit platforms:
    --  typedef int signed_128 __attribute__ ((mode (TI)));