.travis.yml: try to run tests in -mavx2 mode if the CPU supports it

And modify settings so as to hae a AVX2 compatible CPU

.travis.yml

@@ -27,9 +27,11 @@ matrix:
 
 # Test compilation with AVX2
     - os: linux
+      # "sudo: yes" and "dist: trusty" give us a worker with the AVX2 instruction set
+      sudo: yes
+      dist: trusty
       compiler: clang-3.8
-      # skip tests since Travis doesn't have AVX2 compatible machines
-      env: OPJ_CI_CC=clang-3.8 OPJ_CI_CXX=clang-3.8 OPJ_CI_INSTRUCTION_SETS="-mavx2" OPJ_CI_BUILD_CONFIGURATION=Release OPJ_CI_SKIP_TESTS=1
+      env: OPJ_CI_CC=clang-3.8 OPJ_CI_CXX=clang-3.8 OPJ_CI_INSTRUCTION_SETS="-mavx2" OPJ_CI_BUILD_CONFIGURATION=Release
       addons:
         apt:
           sources:

tools/travis-ci/run.sh

@@ -111,6 +111,17 @@ elif [ "${TRAVIS_OS_NAME}" == "linux" ]; then
 	else
 		echo "Compiler not supported: ${CC}"; exit 1
 	fi
+	if [ "${OPJ_CI_INSTRUCTION_SETS-:}" == "-mavx2" ]; then
+		AVX2_AVAIL=1
+		cat /proc/cpuinfo | grep avx2 >/dev/null || AVX2_AVAIL=0
+		if [[ "${AVX2_AVAIL}" == "1" ]]; then
+			echo "AVX2 available on CPU"
+		else
+			echo "AVX2 not available on CPU. Disabling tests"
+			cat /proc/cpuinfo  | grep flags | head -n 1
+			export OPJ_CI_SKIP_TESTS=1
+		fi
+        fi
 elif [ "${TRAVIS_OS_NAME}" == "windows" ]; then
 	OPJ_OS_NAME=windows
 	if which cl > /dev/null; then