MINIFICPP-2117 Fix bustache build in C++20 mode #4358

Job	Run time
windows-2019	2h 7m 55s
centos	1h 24m 16s
Docker build for integration tests	1h 2m 13s
macos-xcode	48m 45s
ubuntu-20.04	38m 55s
ubuntu-20.04-clang	1h 13m 16s
Docker integration tests	28m 40s
	7h 44m 0s

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