add C++20 module #278

Job	Run time
ubuntu cmake	13s
windows (Win32, standard)	1m 17s
macos cmake	13s
windows (Win32, PUGIXML_WCHAR_MODE)	1m 47s
ubuntu (g++, standard)	1m 7s
windows (Win32, PUGIXML_COMPACT)	1m 35s
ubuntu (g++, PUGIXML_WCHAR_MODE)	1m 9s
windows (Win32, PUGIXML_NO_EXCEPTIONS)	1m 52s
ubuntu (g++, PUGIXML_COMPACT)	1m 10s
windows (Win32, PUGIXML_STRING_VIEW)	2m 13s
ubuntu (g++, PUGIXML_NO_EXCEPTIONS)	1m 0s
windows (x64, standard)	1m 47s
ubuntu (g++, PUGIXML_STRING_VIEW)	1m 7s
windows (x64, PUGIXML_WCHAR_MODE)	1m 48s
windows (x64, PUGIXML_COMPACT)	1m 22s
ubuntu (clang++, standard)	52s
windows (x64, PUGIXML_NO_EXCEPTIONS)	1m 21s
ubuntu (clang++, PUGIXML_WCHAR_MODE)	53s
windows (x64, PUGIXML_STRING_VIEW)	2m 5s
ubuntu (clang++, PUGIXML_COMPACT)	56s
ubuntu (clang++, PUGIXML_NO_EXCEPTIONS)	48s
ubuntu (clang++, PUGIXML_STRING_VIEW)	53s
macos (clang++, standard)	46s
macos (clang++, PUGIXML_WCHAR_MODE)	1m 14s
macos (clang++, PUGIXML_COMPACT)	58s
macos (clang++, PUGIXML_NO_EXCEPTIONS)	42s
macos (clang++, PUGIXML_STRING_VIEW)	58s
	32m 6s

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