Travis-CI: Test build with both GCC and Clang (LLVM)

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

.travis.yml

@@ -5,6 +5,11 @@ language: c
 # Use docker for quicker builds, it now allows https://docs.travis-ci.com/user/apt/
 sudo: false
 
+# Test build with both GCC and Clang (LLVM)
+compiler:
+  - gcc
+  - clang
+
 env:
   global:
    # The next declaration is the encrypted COVERITY_SCAN_TOKEN, created