all: fix wildcard to work with make-4.x

In make-3.8x, the $(wildacrd) function would sort the entries,
while in make-4.x, it would just return the entries in any
unpredictable order [*]

Use the $(sort) function to get reproducible behaviour.

[*] Well, most probably the roder the entries appear when read
from readdir()

Reported-by: Andrew Ruder <andrew.ruder@elecsyscorp.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Tested-by: Andrew Ruder <andrew.ruder@elecsyscorp.com>

--- uClibc-0.9.30.orig/extra/scripts/install_headers.sh	2008-10-10 15:50:38.000000000 +0200

+++ uClibc-0.9.30/extra/scripts/install_headers.sh	2011-08-21 09:49:03.000000000 +0200

@@ -33,7 +33,7 @@

 (

 # We must cd, or else we'll prepend "$1" to filenames!

 cd "$1" || exit 1

-find ! -name '.' -a ! -path '*/.*' | sed -e 's/^\.\///' -e '/^config\//d' \

+find . ! -name '.' -a ! -path '*/.*' | sed -e 's/^\.\///' -e '/^config\//d' \

 	-e '/^config$/d'

 ) | \

 (