Add basic Travis config for Linux builds

Performs a single build on Linux using the unified
headers and linking against the ICD.

Unified headers are broken for 2.x on OSX (see
https://github.com/KhronosGroup/OpenCL-Headers/issues/31).
Adding OSX builds should hopefully be a one-line change
once this is fixed.

Signed-off-by: Kevin Petit <kevin.petit@arm.com>

.travis.yml

@@ -0,0 +1,30 @@
+language: cpp
+
+os:
+  - linux
+
+script:
+  - export TOP=$(pwd)
+  - git clone https://github.com/KhronosGroup/OpenCL-Headers.git
+  - cd OpenCL-Headers
+  - ln -s CL OpenCL # For OSX builds
+  - cd ..
+  - git clone https://github.com/KhronosGroup/OpenCL-ICD-Loader.git
+  - cd ${TOP}/OpenCL-ICD-Loader
+  - mkdir build
+  - cd build
+  - cmake -DOPENCL_INCLUDE_DIRS=${TOP}/OpenCL-Headers/ ..
+  - make
+  - cd ${TOP}
+  - git clone https://github.com/KhronosGroup/libclcxx.git
+  - ls -l
+  - mkdir build
+  - cd build
+  - cmake -DCL_INCLUDE_DIR=${TOP}/OpenCL-Headers
+          -DCL_LIB_DIR=${TOP}/OpenCL-ICD-Loader/build/lib
+          -DCL_LIBCLCXX_DIR=${TOP}/libclcxx
+          -DCL_OFFLINE_COMPILER=/dummy/path/to/compiler
+          -DCMAKE_RUNTIME_OUTPUT_DIRECTORY=./bin
+          -DOPENCL_LIBRARIES="-lOpenCL -lpthread"
+          ..
+  - make -j2