Build the samples on the CI services

Requires libomp on macOS from homebrew. OpenMP with Visual C/C++ requires
the loop index to be a signed type (from OpenMP < 3.0).

.travis.yml

@@ -23,6 +23,7 @@ addons:
     - scons
     - boost
     - python
+    - libomp
   ssh_known_hosts:
     - cantera.org
 
@@ -50,6 +51,7 @@ script: |
       set -e
       scons build -j2 python_cmd=/usr/bin/python3 VERBOSE=y python_package=full blas_lapack_libs=lapack,blas optimize=n coverage=y
       scons test
+      scons samples
       scons build sphinx_docs=y doxygen_docs=y sphinx_cmd="/usr/bin/python3 `which sphinx-build`"
       if [[ "${TRAVIS_PULL_REQUEST}" == "false" ]] && [[ "${TRAVIS_BRANCH}" == "master" ]] && [[ "${TRAVIS_REPO_SLUG}" == "Cantera/cantera" ]]; then
         openssl aes-256-cbc -k "${ctdeploy_pass}" -in ./doc/ctdeploy_key.enc -out ./doc/ctdeploy_key -d
@@ -75,6 +77,7 @@ script: |
   else
       scons build -j2 python_cmd=python3 VERBOSE=y python_package=full blas_lapack_libs=lapack,blas optimize=n coverage=y
       scons test
+      scons samples
   fi
 after_success: |
   if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then

appveyor.yml

@@ -11,6 +11,7 @@ install:
 
 build_script:
 - cmd: C:\Python37-x64\Scripts\scons build -j2 boost_inc_dir=C:\Libraries\boost_1_62_0 debug=n VERBOSE=y python_package=full
+- cmd: C:\Python37-x64\Scripts\scons samples
 
 test_script:
 - ps: |

samples/cxx/openmp_ignition/openmp_ignition.cpp

@@ -51,7 +51,7 @@ void run()
     // thread in cases where the workload is biased, e.g. calculations for low
     // T0 take longer than calculations for high T0.
     #pragma omp parallel for schedule(static, 1)
-    for (size_t i = 0; i < nPoints; i++) {
+    for (int i = 0; i < nPoints; i++) {
         // Get the Cantera objects that were initialized for this thread
         size_t j = omp_get_thread_num();
         IdealGasMix& gas = *gases[j];