lt(1): Use 'find -s' instead of 'find | sort'.
This diff of the old behavior vs. new shows the issue:
--- /tmp/t1 2020-03-29 10:09:50.
009490000 +0200
+++ /tmp/t2 2020-03-29 10:10:09.
909695000 +0200
@@ -48,12 +48,12 @@
| |-- SimpleTextOut.h
| `-- UgaDraw.h
|-- Uefi
- |-- Uefi.h
| |-- UefiBaseType.h
| |-- UefiGpt.h
| |-- UefiInternalFormRepresentation.h
| |-- UefiMultiPhase.h
| |-- UefiPxe.h
| `-- UefiSpec.h
+ |-- Uefi.h
`-- X64
`-- ProcessorBind.h
With 'find | sort', lt(1) would incorrectly show the contents of the
'Uefi' directory below the 'Uefi.h' file.
With 'find -s', the 'Uefi.h' file is correctly sorted below 'Uefi'
and its contents.