style: normalize filename in SortedIncludes.fix()

style: normalize filename in SortedIncludes.fix()

The filename affects the sorting result. Therefore check(),
which normalizes the filename, detects an invalid sorting
of includes, but fix() fails to fix the corresponding includes.

Change-Id: I7d5a941c9ebea853004922d19e3b84f8ded2afa6
Signed-off-by: Georg Kotheimer <georg.kotheimer@mailbox.tu-dresden.de>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/10742
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>