clang

Merge branch 'pull-request/#777-Allow-Building-Tests-as-Submodule-and… #636

Job	Run time
Clang C++17 Linux - STL (ubuntu-22.04)	6m 10s
Clang C++11 Linux - STL (ubuntu-22.04)	8m 30s
Clang C++14 Linux - STL (ubuntu-22.04)	5m 47s
Clang C++20 Linux - STL (ubuntu-22.04)	1m 18s
Clang C++20 Linux - No STL (ubuntu-22.04)	1m 11s
Clang C++20 Linux - STL - Force C++03 (ubuntu-22.04)	1m 31s
Clang C++20 Linux - No STL - Force C++03 (ubuntu-22.04)	1m 40s
Clang C++20 OSX - No STL (macos-12)	5m 49s
Clang C++20 OSX - STL (macos-12)	9m 34s
Clang C++20 OSX - STL - Force C++03 (macos-12)	9m 50s
Clang C++20 OSX - No STL - Force C++03 (macos-12)	5m 14s
	56m 34s

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