Add OS X to Travis build

.travis.yml

@@ -2,6 +2,12 @@ language: c
 
 cache: apt
 
+sudo: false
+
+os:
+  - linux
+  - osx
+
 compiler:
   - gcc
 #  - clang
@@ -12,6 +18,10 @@ before_script:
 #  - export PATH=$PWD/gcc-arm-none-eabi-5_3-2016q1/bin:$PATH
   - export CFLAGS="-Wall -Wextra -Werror"
 
+before_install:
+  - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew update; fi
+  - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew install libusb; fi
+
 script:
   - mkdir host/build
   - cd host/build