Add memory fence helper for coroutine resumption #263

Job	Run time
Changelog Summary	24s
Antora Docs	1m 10s
Apple-Clang (macOS 15, asan+ubsan): C++20	2m 36s
GCC 15: C++20	8m 25s
MinGW: C++20	8m 30s
Apple-Clang (macOS 14): C++20	3m 59s
Clang 20: C++20-23 (x86)	6m 33s
Clang 17: C++20	3m 45s
GCC 15: C++20 (asan+ubsan)	8m 28s
MSVC 14.42: C++20	8m 2s
GCC 12: C++20	3m 49s
Clang 20: C++20 (asan+ubsan)	5m 1s
GCC 13: C++20 (coverage)	2m 48s
Clang 20: C++20-23	8m 27s
MSVC 14.34: C++20 (shared)	8m 1s
	1h 19m 58s

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