Test build with LLVM and Subzero backend.

Change-Id: Ic8e2360c044aac47447f6a7ae7071d4e3b181678
Reviewed-on: https://swiftshader-review.googlesource.com/10148
Tested-by: Nicolas Capens <capn@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
diff --git a/.travis.yml b/.travis.yml
index 289ac7c..92e428f 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -8,8 +8,12 @@
   - clang
   - gcc
 
+env:
+  - REACTOR_BACKEND=LLVM
+  - REACTOR_BACKEND=Subzero
+
 script:
   - $CXX --version
-  - mkdir build
-  - cd build
-  - cmake .. && make
\ No newline at end of file
+  - mkdir build && cd build
+  - cmake -DREACTOR_BACKEND=$REACTOR_BACKEND ..
+  - make
\ No newline at end of file