CI: scripts: build curl with ECH support

Add a script to build curl with ECH support, to specify the path of the
openssl+ECH library, you should set the SSL_LIB variable with the prefix
of the library.

Example:
   SSL_LIB=/opt/openssl-ech CURL_DESTDIR=/opt/curl-ech/ ./build-curl.sh

scripts/build-curl.sh

@@ -0,0 +1,48 @@
+#!/bin/sh
+#
+# Download curl and compile it with ECH
+#
+set -eux
+
+CURL_DESTDIR=${CURL_DESTDIR:-${HOME}/opt}
+CURL_TMPDIR=${CURL_TMPDIR:-/tmp/download-cache}
+SSL_LIB=${SSL_LIB:-}
+CURL_VERSION=git-master
+
+SSL_OPT=--with-openssl
+SSL_LDFLAGS=
+
+
+curl_download() {
+	cd "${CURL_TMPDIR}"
+	# update the curl version using the commit ID of the branch HEAD
+	branch_name="${CURL_VERSION##git-}"
+	CURL_VERSION=git-$(wget -q -O- "https://api.github.com/repos/curl/curl/branches/$branch_name" | grep '"sha":' | head -n 1 | sed -E 's/ *"sha": "(.*)",/\1/')
+	wget -q -O "${CURL_TMPDIR}/curl-${CURL_VERSION}.tar.gz" \
+	     "https://github.com/curl/curl/archive/${CURL_VERSION##git-}.tar.gz"
+}
+
+curl_build() {
+	if [ -n "$SSL_LIB" ]; then
+		SSL_LDFLAGS="-Wl,-rpath,${SSL_LIB}/lib"
+		SSL_OPT="--with-ssl=${SSL_LIB}"
+	fi
+
+	cd "${CURL_TMPDIR}"
+	mkdir -p "${CURL_TMPDIR}/curl-${CURL_VERSION}"
+	tar zxf "${CURL_TMPDIR}/curl-${CURL_VERSION}.tar.gz" -C "${CURL_TMPDIR}/curl-${CURL_VERSION}/" --strip-components=1
+	cd "${CURL_TMPDIR}/curl-${CURL_VERSION}"
+
+	autoreconf -fi
+	LDFLAGS=${SSL_LDFLAGS} ./configure "${SSL_OPT}" --prefix="${CURL_DESTDIR}" --enable-ech
+	make -j"$(nproc)"
+	make install
+	echo "${CURL_VERSION}" > "${CURL_DESTDIR}/.curl-version"
+}
+
+
+mkdir -p "${CURL_DESTDIR}"
+mkdir -p "${CURL_TMPDIR}"
+
+curl_download
+curl_build