Iron out some problems in jtagmkII #2620

Job	Run time
linux-x86_64	1m 33s
linux-x86_64-autotools	1m 28s
linux (i386, i686, i686-linux-gnu, i386-linux-gnu)	1m 18s
macos-x86_64	1m 0s
linux (armhf, armhf, arm-linux-gnueabihf, arm-linux-gnueabihf)	1m 20s
macos-x86_64_autotools	58s
linux (arm64, aarch64, aarch64-linux-gnu, aarch64-linux-gnu)	1m 25s
mingw (mingw64, x86_64)	3m 33s
msvc (x86, Win32)	1m 57s
mingw (ucrt64, ucrt-x86_64)	3m 44s
msvc (x64, x64)	1m 40s
mingw (clang64, clang-x86_64)	2m 52s
msvc (arm64, ARM64)	1m 54s
	24m 42s

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