Feature: WCH RISC-V support #1908

Job	Run time
build-linux (ubuntu-20.04, focal, clang-15, 12.2.Rel1)	3m 46s
build-mingw (windows-2022, ucrt64)	3m 16s
build-mingw (windows-2022, clang64)	2m 23s
build-linux (ubuntu-20.04, focal, gcc-11, 12.2.Rel1)	4m 5s
size-diff	44s
build-linux (focal, 96b_carbon	39s
build-linux (focal, bluepill	33s
build-linux (focal, f072	37s
build-linux (focal, f3	33s
build-linux (focal, f4discovery	37s
build-linux (focal, hydrabus	33s
build-linux (focal, launchpad-icdi	46s
build-linux (focal, native	34s
build-linux (focal, stlink	40s
build-linux (focal, stlinkv3	41s
build-linux (focal, swlink	36s
	21m 3s

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