BaseTools/CommonLib: use explicit 64-bit type in Strtoi()

Don't use the native word size string to number parsing routines,
but instead, use the 64-bit one and cast to UINTN.

Currently, the only user is in Source/C/DevicePath/DevicePathFromText.c
which takes care to use Strtoi64 () unless it assumes the value fits
in 32-bit, so this change is a no-op even on 32-bit build hosts.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

BaseTools/Source/C/Common/CommonLib.c

@@ -2252,9 +2252,9 @@ Strtoi (
   )
 {
   if (IsHexStr (Str)) {
-    return StrHexToUintn (Str);
+    return (UINTN)StrHexToUint64 (Str);
   } else {
-    return StrDecimalToUintn (Str);
+    return (UINTN)StrDecimalToUint64 (Str);
   }
 }