Adding C++20 tests.

Author: lemire

.github/workflows/ubuntu20-cxx20.yml

@@ -0,0 +1,19 @@
+name: Ubuntu 20.04 CI (C++20)
+
+on: [push, pull_request]
+
+jobs:
+  ubuntu-build:
+    runs-on: ubuntu-20.04
+    strategy:
+      fail-fast: false
+    steps:
+      - uses: actions/checkout@v2
+      - name: Use cmake
+        run: |
+          mkdir build &&
+          cd build &&
+          cmake -DCMAKE_CXX_STANDARD=20 -DFASTFLOAT_TEST=ON -DCMAKE_INSTALL_PREFIX:PATH=destination ..  &&
+          cmake --build .   &&
+          ctest --output-on-failure  &&
+          cmake --install .

.github/workflows/ubuntu20.yml

@@ -1,4 +1,4 @@
-name: Ubuntu 20.04 CI (GCC 9, 8)
+name: Ubuntu 20.04 CI (GCC 9)
 
 on: [push, pull_request]
 
@@ -26,4 +26,4 @@ jobs:
           cd ../tests/installation_tests/find &&
           mkdir build && cd build && cmake -DCMAKE_INSTALL_PREFIX:PATH=../../../build/destination .. &&  cmake --build . &&
           cd ../../issue72_installation  &&
-          mkdir build && cd build && cmake -DCMAKE_INSTALL_PREFIX:PATH=../../../build/destination .. &&  cmake --build .
+          mkdir build && cd build && cmake -DCMAKE_INSTALL_PREFIX:PATH=../../../build/destination .. &&  cmake --build .

CMakeLists.txt

@@ -2,7 +2,7 @@ cmake_minimum_required(VERSION 3.9)
 
 project(fast_float VERSION 2.0.0 LANGUAGES CXX)
 option(FASTFLOAT_TEST "Enable tests" OFF)
-set(CMAKE_CXX_STANDARD 11)
+set(CMAKE_CXX_STANDARD 11 CACHE STRING "C++ standard to be used")
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 if(FASTFLOAT_TEST)
   enable_testing()