travis: add Clang builds

PX4 isn't supported at the moment and sitltest always use GCC, so we include the only ones that build
Travis has old LLVM installed and old Clang in a strange path (not a package) which interfere with the use of clang-3.7

.travis.yml

@@ -16,6 +16,7 @@ addons:
     branch_pattern: coverity_scan
 
 before_install:
+  - export PATH=$(echo ${PATH} | awk -v RS=':' -v ORS=':' '/clang/ {next} {print}' | sed 's/:*$//')
   - APMDIR=$(pwd) && pushd .. && $APMDIR/Tools/scripts/configure-ci.sh && . ~/.profile && popd
 
 script:
@@ -30,6 +31,8 @@ notifications:
     on_failure: always  # options: [always|never|change] default: always
     on_start: false     # default: false
 
+compiler: gcc
+
 env:
   global:
     # The next declaration is the encrypted COVERITY_SCAN_TOKEN, created
@@ -39,3 +42,10 @@ env:
     - CI_BUILD_TARGET="px4-v2 sitl linux"
     - CI_BUILD_TARGET="navio raspilot minlure bebop"
     - CI_BUILD_TARGET="sitltest"
+
+matrix:
+  include:
+    - compiler: clang
+      env: CI_BUILD_TARGET="sitl linux minlure"
+    - compiler: clang
+      env: CI_BUILD_TARGET="navio raspilot bebop"

Tools/scripts/configure-ci.sh

@@ -25,6 +25,7 @@ fi
 wget -q -O - http://llvm.org/apt/llvm-snapshot.gpg.key | sudo apt-key add -
 sudo add-apt-repository "deb http://llvm.org/apt/${UBUNTU_CODENAME}/ llvm-toolchain-${UBUNTU_CODENAME}-3.7 main" -y
 sudo apt-get -qq -y update
+sudo apt-get -qq -y remove clang llvm
 sudo apt-get -y install $PKGS
 sudo update-alternatives --install /usr/bin/clang clang /usr/bin/clang-3.7 37 \
     --slave /usr/bin/clang++ clang++ /usr/bin/clang++-3.7