CI: Add a new stage to check languages

.github/travis/cmake-lang.sh

@@ -0,0 +1,10 @@
+#!/bin/sh
+set -xe
+rm -rf build
+mkdir build
+cd build
+cmake .. \
+    -DCMAKE_TOOLCHAIN_FILE="../cmake/AvrGcc.cmake" \
+    -DCMAKE_BUILD_TYPE=Release \
+    -G Ninja
+ninja check_lang

.travis.yml

@@ -37,7 +37,12 @@ jobs:
     - stage: tests
       script: ./.github/travis/cmake-test.sh
 
+    # language checks
+    - stage: lang
+      script: ./.github/travis/cmake-lang.sh
+
 stages:
   - cmake
+  - lang
   - legacy
   - tests