efi: look for headers and libs in the sysroot

Currently, syslinux hard-codes search paths to /usr/.... directories.
This does not play well in cross-compilation.

If $SYSROOT is defined, prepend it to the search paths.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

diff -durN syslinux-6.02.orig/efi/find-gnu-efi.sh syslinux-6.02/efi/find-gnu-efi.sh
--- syslinux-6.02.orig/efi/find-gnu-efi.sh	2013-10-13 19:59:03.000000000 +0200
+++ syslinux-6.02/efi/find-gnu-efi.sh	2014-04-22 00:19:23.638483887 +0200
@@ -9,7 +9,7 @@
 find_include()
 {
     for d in $include_dirs; do
-	found=`find $d -name efi -type d 2> /dev/null`
+	found=`find $SYSROOT$d -name efi -type d 2> /dev/null`
 	if [ "$found"x != "x" ] && [ -e $found/$ARCH/efibind.h ]; then
 	    echo $found
 	    break;
@@ -20,12 +20,12 @@
 find_lib()
 {
     for d in $lib_dirs; do
-	found=`find $d -name libgnuefi.a 2> /dev/null`
+	found=`find $SYSROOT$d -name libgnuefi.a 2> /dev/null`
 	if [ "$found"x != "x" ]; then
 	    crt_name='crt0-efi-'$ARCH'.o'
-	    crt=`find $d -name $crt_name 2> /dev/null`
+	    crt=`find $SYSROOT$d -name $crt_name 2> /dev/null`
 	    if [ "$crt"x != "x" ]; then
-		echo $d
+		echo $SYSROOT$d
 		break;
 	    fi
 	fi