Add build script and manifest for GNU Hello

https://www.gnu.org/software/hello/

build.sh

+#!/bin/sh
+
+FILE=org.gnu.hello.json
+VERSION=2.10
+
+APPID=`basename $FILE .json`
+
+if [ x$TARGET != x`uname -p` -a ! -z "$TARGET" ]; then
+	if [ ! -x qemu-static ]; then
+		echo "QEmu static emulator missing as 'qemu-static' executable"
+		exit 1
+	fi
+
+	ARCH_OPT="--arch=$TARGET"
+	ARCH_EMU_OPT="--arch-emulator=`pwd`/qemu-static"
+else
+	TARGET=`uname -p`
+fi
+
+echo ========== Building $APPID ================
+rm -rf app
+flatpak-builder $ARCH_OPT $ARCH_EMU_OPT --ccache --require-changes --repo=hello-repo --subject="${APPID} ${VERSION}" ${EXPORT_ARGS-} app $FILE && \
+flatpak build-bundle $ARCH_OPT hello-repo/ $APPID.$TARGET.xdgapp $APPID master

org.gnu.hello.json

+{
+    "app-id": "org.gnu.hello",
+    "runtime": "org.freedesktop.Platform",
+    "runtime-version": "1.4",
+    "sdk": "org.freedesktop.Sdk",
+    "command": "hello",
+    "separate-locales": false,
+    "build-options" : {
+        "cflags": "-O2 -g",
+        "cxxflags": "-O2 -g"
+    },
+    "cleanup": [ "/bin/flatpak-arch-emulator" ],
+    "modules": [
+        {
+            "name": "gnu-hello",
+            "sources": [
+                {
+                    "type": "archive",
+                    "url": "http://ftp.gnu.org/gnu/hello/hello-2.10.tar.gz",
+                    "sha256": "31e066137a962676e89f69d1b65382de95a7ef7d914b8cb956f41ea72e0f516b"
+                }
+            ]
+        }
+    ]
+}