Ports: Add libsixel

This contains `img2sixel`.

Ports/libsixel/package.sh

@@ -0,0 +1,11 @@
+#!/usr/bin/env -S bash ../.port_include.sh
+port=libsixel
+version=1.8.6
+files="https://github.com/saitoha/libsixel/archive/refs/tags/v${version}.tar.gz ${port}-${version}.tar.gz 37611d60c7dbcee701346967336dbf135fdd5041024d5f650d52fae14c731ab9"
+useconfigure=true
+auth_type=sha256
+configopts="--prefix=${SERENITY_INSTALL_ROOT}/usr/local"
+
+install() {
+    run make install
+}

Ports/libsixel/patches/config.sub.patch

@@ -0,0 +1,13 @@
+diff --git a/config.sub b/config.sub
+index 9ccf09a..3f638ab 100755
+--- a/config.sub
++++ b/config.sub
+@@ -1390,7 +1390,7 @@ case $os in
+ 	      | -powermax* | -dnix* | -nx6 | -nx7 | -sei* | -dragonfly* \
+ 	      | -skyos* | -haiku* | -rdos* | -toppers* | -drops* | -es* \
+ 	      | -onefs* | -tirtos* | -phoenix* | -fuchsia* | -redox* | -bme* \
+-	      | -midnightbsd*)
++	      | -midnightbsd* | -serenity*)
+ 	# Remember, each alternative MUST END IN *, to match a version number.
+ 		;;
+ 	-qnx*)