remove xcode

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>

.travis.yml

@@ -63,15 +63,7 @@ env:
     # Static build. Note we have disable building the bindings because they won't work with a static libz3
     - LINUX_BASE=ubuntu_16.04 C_COMPILER=/usr/bin/gcc-5 CXX_COMPILER=/usr/bin/g++-5 TARGET_ARCH=x86_64 Z3_STATIC_BUILD=1 DOTNET_BINDINGS=0 JAVA_BINDINGS=0 PYTHON_BINDINGS=0
 
-# macOS (a.k.a OSX) support
-matrix:
-  include:
-    # For now just test a single configuration. macOS builds on TravisCI are
-    # very slow so we should keep the number of configurations we test on this
-    # OS to a minimum.
-    - os: osx
-      osx_image: xcode9.2
-      env: Z3_BUILD_TYPE=RelWithDebInfo DOTNET_BINDINGS=0
+
 script:
   # Use `travis_wait` when doing LTO builds because this configuration will
   # have long link times during which it will not show any output which

src/api/c++/z3++.h

@@ -2309,6 +2309,8 @@ namespace z3 {
         }
 
         friend std::ostream & operator<<(std::ostream & out, model const & m);
+
+        std::string to_string() const { return std::string(Z3_model_to_string(ctx(), m_model); }
     };
     inline std::ostream & operator<<(std::ostream & out, model const & m) { out << Z3_model_to_string(m.ctx(), m); return out; }