Travis clang fix on OSX

.travis.yml

@@ -5,17 +5,25 @@ cache:
   directories:
    - $HOME/deps
 
-rust:
-  - stable
-  - nightly
-os:
-  - linux
-  - osx
+matrix:
+  include:
+    - os: linux
+      rust: stable
+    - os: linux
+      rust: nightly
+    - os: osx
+      rust: stable
+      osx_image: xcode9
+      compiler: clang
+    - os: osx
+      rust: nightly
+      osx_image: xcode9
+      compiler: clang
+
 branches:
   except:
     - staging.tmp
 
-
 notifications:
   webhooks:
     urls:
@@ -33,7 +41,7 @@ before_install:
   # (assuming it will have libsdl2-dev and Rust by then)
   # see https://docs.travis-ci.com/user/trusty-ci-environment/
   - if [[ $TRAVIS_OS_NAME == "linux" ]]; then export DISPLAY=:99.0 && sh -e /etc/init.d/xvfb start && make travis-sdl2; fi
-  - if [[ $TRAVIS_OS_NAME == osx ]]; then brew update && brew install sdl2 && brew upgrade cmake; fi
+  - if [[ $TRAVIS_OS_NAME == osx ]]; then brew update && brew install sdl2 && brew upgrade cmake && export CXX=clang++ && export CC=clang && export MACOSX_DEPLOYMENT_TARGET=10.7; fi
 
 addons:
   apt:

src/backend/metal/Cargo.toml

@@ -29,4 +29,4 @@ cocoa = "0.9"
 core-foundation = "0.3"
 core-graphics = "0.9"
 io-surface = "0.7"
-spirv_cross = "0.3"
+spirv_cross = { git = "https://github.com/grovesNL/spirv_cross.git", branch = "build-set-stdlib" }