ci: add clang-cxx17 toolchain

.travis.yml

@@ -63,6 +63,13 @@ matrix:
         BUILD_RELEASE=bionic
         BUILD_ARCH=amd64
         TOOLCHAIN=gcc-cxx17
+    - os: linux
+      env: >
+        BUILD_FLAVOR=ubuntu
+        BUILD_RELEASE=bionic
+        BUILD_ARCH=amd64
+        TOOLCHAIN=clang-cxx17
+        BUILD_PACKAGES="cmake clang"
     # } // end Linux
 
     # Windows build with mingw-w64 on Ubuntu 18.04

toolchains/clang-cxx17.cmake

+# Sample toolchain file for building with gcc compiler
+#
+# Typical usage:
+#    *) cmake -H. -B_build -DCMAKE_TOOLCHAIN_FILE="${PWD}/toolchains/gcc.cmake"
+
+# set compiler
+set(CMAKE_C_COMPILER clang)
+set(CMAKE_CXX_COMPILER clang++)
+
+# set c++ standard
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+set(CMAKE_CXX_EXTENSIONS OFF)