CMake won't find the right Python 2.7, so tell it where it is.

.travis.yml

@@ -71,8 +71,7 @@ before_script:
 script:
 - >
   if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then
-    cmake -DHAVE_CARBON=NO -DOPENSSL_ROOT_DIR=/usr/local/Cellar/openssl/1.0.2o_1 \
-    -DBUILD_METALIBS=$BUILD_METALIBS -DCOMPOSITE_SOURCE_LIMIT=$COMPOSITE_SOURCE_LIMIT ..;
+    ../.travis/script_macos.sh;
   else
     cmake -DHAVE_GTK2=NO -DBUILD_METALIBS=$BUILD_METALIBS \
     -DCOMPOSITE_SOURCE_LIMIT=$COMPOSITE_SOURCE_LIMIT ..;

.travis/install_macos.sh

@@ -5,5 +5,5 @@ wxmac opencv assimp libvorbis [email protected] || true
 brew install ode --with-shared
 
 # We can't trust brew to make the right symlinks, so execute commands as modules
-/usr/local/bin/${PYTHON_INTERP:-python3} -m pip install virtualenv
-/usr/local/bin/${PYTHON_INTERP:-python3} -m virtualenv venv
+${PYTHON_INTERP:-python3} -m pip install virtualenv
+${PYTHON_INTERP:-python3} -m virtualenv venv

.travis/script_macos.sh

@@ -0,0 +1,9 @@
+#!/bin/bash
+
+if [[ "$PYTHON_INTERP" == "python2.7" ]]; then
+  export PY2_CMAKE_ARGS="-DPYTHON_EXECUTABLE=/usr/local/bin/python -DPYTHON_LIBRARY=/usr/local/opt/python@2/Frameworks/Python.framework/Versions/2.7/lib/libpython2.7.dylib"
+fi
+
+cmake -DHAVE_CARBON=NO -DOPENSSL_ROOT_DIR=/usr/local/Cellar/openssl/1.0.2o_1 \
+-DBUILD_METALIBS=$BUILD_METALIBS -DCOMPOSITE_SOURCE_LIMIT=$COMPOSITE_SOURCE_LIMIT \
+$PY2_CMAKE_ARGS ..