app-arch/atool: fix bashism in configure script

Closes: https://bugs.gentoo.org/775158
Signed-off-by: Sam James <sam@gentoo.org>

app-arch/atool/atool-0.39.0-r1.ebuild

@@ -1,8 +1,10 @@
-# Copyright 1999-2019 Gentoo Authors
+# Copyright 1999-2021 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2
 
 EAPI=7
 
+inherit autotools
+
 DESCRIPTION="Script for managing file archives of various types"
 HOMEPAGE="https://www.nongnu.org/atool/"
 SRC_URI="https://savannah.nongnu.org/download/${PN}/${P}.tar.gz"
@@ -14,3 +16,14 @@ KEYWORDS="amd64 ppc x86"
 DEPEND="dev-lang/perl"
 RDEPEND="${DEPEND}
 	!app-text/adiff"
+
+PATCHES=(
+	"${FILESDIR}"/${PN}-0.39.0-configure-bashism.patch
+)
+
+src_prepare() {
+	default
+
+	# Needed for the bashism patch
+	eautoreconf
+}

app-arch/atool/files/atool-0.39.0-configure-bashism.patch

@@ -0,0 +1,12 @@
+https://bugs.gentoo.org/775158
+--- a/configure.ac
++++ b/configure.ac
+@@ -11,7 +11,7 @@ AC_DEFINE_DIR(LOCALSTATEDIR, localstatedir)
+ dnl Perl stuff
+ AC_PATH_PROG([PERL], [perl])
+ eval `$PERL -V:startperl`
+-if test "${startperl:0:1}" = "#" ; then
++if test "$(printf %.1s "$startperl")" = "#" ; then
+   startperl="\\$startperl"
+ fi
+ AC_SUBST(PERL_SHEBANG, $startperl)