add C++20 module #280

Job	Run time
ubuntu cmake	13s
windows (Win32, standard)	1m 54s
macos cmake	19s
ubuntu (g++, standard)	1m 7s
windows (Win32, PUGIXML_WCHAR_MODE)	1m 46s
ubuntu (g++, PUGIXML_WCHAR_MODE)	1m 7s
windows (Win32, PUGIXML_COMPACT)	1m 17s
ubuntu (g++, PUGIXML_COMPACT)	1m 8s
windows (Win32, PUGIXML_NO_EXCEPTIONS)	1m 45s
ubuntu (g++, PUGIXML_NO_EXCEPTIONS)	1m 3s
windows (Win32, PUGIXML_STRING_VIEW)	1m 13s
ubuntu (g++, PUGIXML_STRING_VIEW)	1m 8s
windows (x64, standard)	1m 14s
ubuntu (clang++, standard)	49s
windows (x64, PUGIXML_WCHAR_MODE)	1m 15s
ubuntu (clang++, PUGIXML_WCHAR_MODE)	55s
windows (x64, PUGIXML_COMPACT)	2m 1s
windows (x64, PUGIXML_NO_EXCEPTIONS)	2m 24s
ubuntu (clang++, PUGIXML_COMPACT)	54s
windows (x64, PUGIXML_STRING_VIEW)	1m 16s
ubuntu (clang++, PUGIXML_NO_EXCEPTIONS)	46s
ubuntu (clang++, PUGIXML_STRING_VIEW)	49s
macos (clang++, standard)	44s
macos (clang++, PUGIXML_WCHAR_MODE)	54s
macos (clang++, PUGIXML_COMPACT)	59s
macos (clang++, PUGIXML_NO_EXCEPTIONS)	44s
macos (clang++, PUGIXML_STRING_VIEW)	55s
	30m 39s

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