Misc warning fixes

Author: Fabien-Chouteau

arch/ARM/cortex_m/src/semihosting-filesystem.adb

@@ -394,6 +394,10 @@ package body Semihosting.Filesystem is
    function Flush
      (This : in out SHFS_File_Handle)
       return Status_Code
-   is (OK);
+   is
+      pragma Unreferenced (This);
+   begin
+      return OK;
+   end Flush;
 
 end Semihosting.Filesystem;

arch/RISC-V/SiFive/drivers/fe310-time.adb

@@ -32,7 +32,6 @@
 --                                                                          --
 ------------------------------------------------------------------------------
 
-with FE310; use FE310;
 with FE310.CLINT; use FE310.CLINT;
 
 package body FE310.Time is