add C++20 module #270

Job	Run time
ubuntu cmake	11s
windows (Win32, standard)	1m 58s
macos cmake	19s
windows (Win32, PUGIXML_WCHAR_MODE)	1m 35s
ubuntu (g++, standard)	1m 8s
windows (Win32, PUGIXML_COMPACT)	2m 19s
ubuntu (g++, PUGIXML_WCHAR_MODE)	1m 8s
windows (Win32, PUGIXML_NO_EXCEPTIONS)	1m 44s
ubuntu (g++, PUGIXML_COMPACT)	1m 12s
windows (Win32, PUGIXML_STRING_VIEW)	1m 9s
ubuntu (g++, PUGIXML_NO_EXCEPTIONS)	1m 0s
windows (x64, standard)	2m 3s
ubuntu (g++, PUGIXML_STRING_VIEW)	1m 11s
windows (x64, PUGIXML_WCHAR_MODE)	1m 47s
ubuntu (clang++, standard)	54s
windows (x64, PUGIXML_COMPACT)	1m 44s
windows (x64, PUGIXML_NO_EXCEPTIONS)	1m 59s
ubuntu (clang++, PUGIXML_WCHAR_MODE)	56s
windows (x64, PUGIXML_STRING_VIEW)	2m 4s
ubuntu (clang++, PUGIXML_COMPACT)	51s
ubuntu (clang++, PUGIXML_NO_EXCEPTIONS)	48s
ubuntu (clang++, PUGIXML_STRING_VIEW)	57s
macos (clang++, standard)	1m 10s
macos (clang++, PUGIXML_WCHAR_MODE)	45s
macos (clang++, PUGIXML_COMPACT)	52s
macos (clang++, PUGIXML_NO_EXCEPTIONS)	1m 14s
macos (clang++, PUGIXML_STRING_VIEW)	47s
	33m 45s

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