fix: determine legacy variant after determining compiler version #404

Job	Run time
Syntax Check - Clang C++03 Linux No STL (ubuntu-22.04)	46s
Syntax Check - Clang C++03 Linux STL (ubuntu-22.04)	51s
Syntax Check - Clang C++11 Linux No STL (ubuntu-22.04)	1m 19s
Syntax Check - Clang C++11 Linux No STL Force C++03 (ubuntu-22.04)	1m 10s
Syntax Check - Clang C++11 Linux STL (ubuntu-22.04)	1m 16s
Syntax Check - Clang C++14 Linux No STL (ubuntu-22.04)	1m 10s
Syntax Check - Clang C++11 Linux STL Force C++03 (ubuntu-22.04)	1m 12s
Syntax Check - Clang C++14 Linux No STL Force C++03 (ubuntu-22.04)	1m 16s
Syntax Check - Clang C++14 Linux STL (ubuntu-22.04)	1m 16s
Syntax Check - Clang C++14 Linux STL Force C++03 (ubuntu-22.04)	1m 22s
Syntax Check - Clang C++17 Linux No STL (ubuntu-22.04)	1m 27s
Syntax Check - Clang C++17 Linux No STL Force C++03 (ubuntu-22.04)	1m 34s
Syntax Check - Clang C++17 Linux STL (ubuntu-22.04)	2m 9s
Syntax Check - Clang C++17 Linux STL Force C++03 (ubuntu-22.04)	1m 45s
Syntax Check - Clang C++20 Linux No STL (ubuntu-22.04)	2m 1s
Syntax Check - Clang C++20 Linux No STL Force C++03 (ubuntu-22.04)	2m 3s
Syntax Check - Clang C++20 Linux STL (ubuntu-22.04)	2m 40s
Syntax Check - Clang C++20 Linux STL Force C++03 (ubuntu-22.04)	2m 37s
	27m 54s

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