travis: add osx build with darwinssl

Closes #1706

.travis.yml

@@ -32,10 +32,13 @@ matrix:
           env: BUILD_TYPE=debug
         - os: osx
           compiler: gcc
-          env: BUILD_TYPE=debug CONFIGURE=--with-ssl=/usr/local/opt/openssl
+          env: BUILD_TYPE=debug C=--with-ssl=/usr/local/opt/openssl
         - os: osx
           compiler: gcc
-          env: BUILD_TYPE=debug CONFIGURE=--with-ssl=/usr/local/opt/libressl
+          env: BUILD_TYPE=debug C=--with-ssl=/usr/local/opt/libressl
+        - os: osx
+          compiler: clang
+          env: BUILD_TYPE=debug C="--without-ssl --with-darwinssl"
         - os: osx
           compiler: clang
           env: BUILD_TYPE=normal
@@ -82,13 +85,13 @@ script:
         fi
     - |
         if [ "$BUILD_TYPE" = "debug" ]; then
-             ./configure --enable-debug --enable-werror $CONFIGURE
+             ./configure --enable-debug --enable-werror $C
              make
              make TFLAGS=-n test-nonflaky
         fi
     - |
         if [ "$BUILD_TYPE" = "normal" ]; then
-             ./configure --enable-warnings --enable-werror
+             ./configure --enable-warnings --enable-werror $C
              make
              make test-nonflaky
         fi