Update .travis.yml

Check that the bare-arm, stmhal and unix-cpy ports at least remain compilable, even if we can only actually run tests against the unix port.

.travis.yml

@@ -4,10 +4,14 @@ compiler:
 
 before_script:
   - sudo add-apt-repository -y ppa:fkrull/deadsnakes
+  - sudo add-apt-repository -y ppa:terry.guo/gcc-arm-embedded
   - sudo apt-get update -qq
-  - sudo apt-get install -y python3.3 python3
+  - sudo apt-get install -y python3.3 python3 gcc-arm-none-eabi
 
 script:
+  - make -C bare-arm
+  - make -C stmhal
+  - make -C unix-cpy
   - make -C unix
   - cd tests && MICROPY_CPYTHON3=python3.3 ./run-tests