net-p2p/rtorrent: fix GREP call for stable version

scripts/common.m4 calls $GREP at configure time.
this can cause problems with slibtool and maybe also split-usr env.

Signed-off-by: Nicolas PARLANT <nicolas.parlant@parhuet.fr>
Part-of: https://github.com/gentoo/gentoo/pull/43457
Closes: https://github.com/gentoo/gentoo/pull/43457
Signed-off-by: Sam James <sam@gentoo.org>

net-p2p/rtorrent/files/rtorrent-0.15.5-find_grep.patch

@@ -0,0 +1,13 @@
+https://github.com/rakshasa/rtorrent/commit/dd8281204f5365f0f6987f989e71208d3c218289
+from upstream
+configure fails with slibtool because it doesn't define GREP
+--- a/scripts/common.m4
++++ b/scripts/common.m4
+@@ -23,6 +23,7 @@ AC_DEFUN([TORRENT_WITH_SYSROOT], [
+ 
+ AC_DEFUN([TORRENT_REMOVE_UNWANTED],
+ [
++  AC_REQUIRE([AC_PROG_GREP])
+   values_to_check=`for i in $2; do echo $i; done`
+   unwanted_values=`for i in $3; do echo $i; done`
+   if test -z "${unwanted_values}"; then

net-p2p/rtorrent/rtorrent-0.15.5.ebuild

@@ -44,6 +44,8 @@ DOCS=( doc/rtorrent.rc )
 
 PATCHES=(
 	"${FILESDIR}"/${PN}-0.15.3-unbundle_json.patch
+	# fix configure w/ slibtool. merged in 0.16.0
+	"${FILESDIR}"/${PN}-0.15.5-find_grep.patch
 )
 
 pkg_setup() {