travis: Run tests against wolfSSL

Check for wolfssl/options.h because if it isn't included, checking other
headers will trigger a warning about hardening the wolfSSL build, which
will cause the check to fail with -Werror.

If the file doesn't exist because user_settings.h is used, the check may
be skipped by configuring with `ac_cv_header_wolfssl_options_h=yes`.

.travis.yml

@@ -81,6 +81,8 @@ matrix:
     # the crypto plugins are build-tested with clang via "all" above
     - env: TEST=botan
     - env: TEST=botan LEAK_DETECTIVE=yes
+    - env: TEST=wolfssl
+    - env: TEST=wolfssl LEAK_DETECTIVE=yes
     - env: TEST=openssl
     - env: TEST=openssl LEAK_DETECTIVE=yes
     - env: TEST=openssl-1.0