community/libepubgen: fix build on riscv64 and modernize

community/libepubgen/APKBUILD

@@ -9,10 +9,15 @@ license="MPL-2.0"
 makedepends="librevenge-dev libxml2-dev doxygen"
 subpackages="$pkgname-dev $pkgname-doc"
 source="https://download.sourceforge.net/project/libepubgen/libepubgen-$pkgver/libepubgen-$pkgver.tar.bz2"
-builddir="$srcdir"/$pkgname-$pkgver
+
+prepare() {
+	default_prepare
+
+	update_config_sub
+	update_config_guess
+}
 
 build() {
-	cd "$builddir"
 	./configure \
 		--build=$CBUILD \
 		--host=$CHOST \
@@ -25,12 +30,10 @@ build() {
 
 
 check() {
-	cd "$builddir"
 	make check
 }
 
 package() {
-	cd "$builddir"
 	make DESTDIR="$pkgdir" install
 }