Add support for modular build structure. #505

Job	Run time
B2 gcc-11	4m 56s
CMake gcc-11 17 Debug	10m 47s
B2 clang-14	5m 7s
CMake gcc-11 20 Release	13m 0s
B2 msvc-14.2	7m 48s
CMake msvc-14.2 Debug C++17	8m 48s
CMake clang-11 17 Debug	7m 10s
B2 msvc-14.3	8m 38s
CMake msvc-14.2 Release C++17	6m 15s
CMake msvc-14.3 Debug C++20	8m 46s
CMake msvc-14.3 Release C++20	6m 21s
CMake clang-11 20 Debug	7m 38s
CMake clang-13 17 Release	10m 23s
CMake clang-13 20 Release	11m 2s
CMake clang-14 17 Debug -stdlib=libc++	9m 49s
CMake clang-14 20 Release -stdlib=libc++	13m 33s
	2h 20m 1s

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