autotools.bbclass: using relative paths for acpaths

Fix autotools.bbclass to use relative paths for acpaths instead of
absolute ones. Since absolute paths may cause potential autoreconf
error like:

    Can't exec "/bin/sh": Argument list too long ...

This error occurs while building coreutils with long TMPDIR, because
it has bunch of m4 files need to be expanded.

[YOCTO #2766]

(From OE-Core rev: aa66ef6598c84231577d139ec7be413e73fac2b1)

Signed-off-by: Wenzong Fan <wenzong.fan@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/autotools.bbclass

@@ -130,7 +130,8 @@ autotools_do_configure() {
 		if [ x"${acpaths}" = xdefault ]; then
 			acpaths=
 			for i in `find ${S} -maxdepth 2 -name \*.m4|grep -v 'aclocal.m4'| \
-				grep -v 'acinclude.m4' | sed -e 's,\(.*/\).*$,\1,'|sort -u`; do
+				grep -v 'acinclude.m4' | sed -e 's,\(.*/\).*$,\1,'|sort -u| \
+				sed -e 's,${S},\.,'`; do
 				acpaths="$acpaths -I $i"
 			done
 		else