LINT: add clang-tidy step (#6295)

* Implement new travis clang-tidy build step

* This step enable some rules and enforce one rule as error
* This permits to have some C++ quality rules based on clang & clang contributor guidelines

* Fix clang-tidy reported problems on push_back -> emplace_back

util/travis/clangtidy.sh

@@ -0,0 +1,27 @@
+if hash clang-tidy-5.0 2>/dev/null; then
+	CLANG_TIDY=clang-tidy-5.0
+else
+	CLANG_TIDY=clang-tidy
+fi
+
+files_to_analyze="$(find src/ -name '*.cpp' -or -name '*.h')"
+
+mkdir -p cmakebuild && cd cmakebuild
+cmake -DCMAKE_BUILD_TYPE=Debug \
+	-DCMAKE_EXPORT_COMPILE_COMMANDS=ON \
+	-DRUN_IN_PLACE=TRUE \
+	-DENABLE_GETTEXT=TRUE \
+	-DENABLE_SOUND=FALSE \
+	-DBUILD_SERVER=TRUE ..
+make GenerateVersion
+cd ..
+
+echo "Performing clang-tidy checks..."
+./util/travis/run-clang-tidy.py -clang-tidy-binary=${CLANG_TIDY} -p cmakebuild \
+	-checks='-*,modernize-use-emplace,modernize-avoid-bind,performance-*' \
+	-warningsaserrors='-*,modernize-use-emplace' \
+	-no-command-on-stdout -quiet \
+	files 'src/.*'
+RET=$?
+echo "Clang tidy returned $RET"
+exit $RET