travis-ci: build libstrophe against LibreSSL

travis/before_script.sh

@@ -0,0 +1,14 @@
+#!/bin/sh
+
+if [ "x$LIBRESSL" = "xyes" ]; then
+    cd "$HOME"
+    git clone https://github.com/libressl-portable/portable.git libressl-git
+    cd libressl-git
+    if [ -n "$LIBRESSL_COMMIT" ]; then
+        git checkout "$LIBRESSL_COMMIT"
+    fi
+    ./autogen.sh
+    ./configure --prefix="$HOME/libressl"
+    make -j"$(nproc)"
+    make install
+fi