travis: add a build using libressl (from git master)

The v3.2.1 tag (latest release atm) results in a broken build.

Closes #5932

.travis.yml

@@ -109,6 +109,9 @@ jobs:
         - libpsl-dev
         - libbrotli-dev
         - libzstd-dev
+  - env:
+    - T=novalgrind LIBRESSL=yes C="--with-ssl=$HOME/libressl" LD_LIBRARY_PATH=/home/travis/libressl/lib:/usr/local/lib
+    - OVERRIDE_CC="CC=gcc-8" OVERRIDE_CXX="CXX=g++-8"
   - env:
     - T=novalgrind NGTCP2=yes C="--with-ssl=$HOME/ngbuild --with-ngtcp2=$HOME/ngbuild --with-nghttp3=$HOME/ngbuild --enable-alt-svc" NOTESTS=
     - OVERRIDE_CC="CC=gcc-8" OVERRIDE_CXX="CXX=g++-8"

scripts/travis/before_script.sh

@@ -98,6 +98,16 @@ if [ "$TRAVIS_OS_NAME" = linux -a "$OPENSSL3" ]; then
   make install_sw
 fi
 
+if [ "$TRAVIS_OS_NAME" = linux -a "$LIBRESSL" ]; then
+  cd $HOME
+  git clone --depth=1 https://github.com/libressl-portable/portable.git libressl-git
+  cd libressl-git
+  ./autogen.sh
+  ./configure --prefix=$HOME/libressl
+  make
+  make install
+fi
+
 if [ "$TRAVIS_OS_NAME" = linux -a "$QUICHE" ]; then
   cd $HOME
   git clone --depth=1 --recursive https://github.com/cloudflare/quiche.git