StdLib: Correct two instances of mismatch between function declaration and definition...

StdLib: Correct two instances of mismatch between function declaration and definition causing GCC compile errors.

StdLib\Include\Containers\Fifo.h
  Change return type of cFIFO_Truncate to size_t.  Makes declaration match definition.
  Update comment to describe what is returned.

StdLib\LibC\Uefi\InteractiveIO\IIOutilities.c
  Change return type of IIO_CursorDelta to int. Makes declaration match definition.
  Change other types from INT32 to int, for consistency.
  Update comment for returned values.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by:  daryl.mcdaniel@intel.com
Reviewed-by:    erik.c.bjorge@intel.com
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@14060 6f19259b-4bc3-4df7-8a09-765794883524