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add code to detect/clean legacy install #11454

Job	Run time
docs / Build linux64	1m 16s
lint / lint	22s
package / Linux / Build linux64	1m 49s
test / Windows MSVC / Build win64	4m 8s
package / Windows / Build win64	4m 52s
test / Linux gcc-11 / Build linux64	1m 46s
test / Linux gcc-12 / Build linux64	1m 45s
check-pr	0s
test / Run Linux test suite / Test (ubuntu, gcc-11, default plugins, default config)	51s
test / Run Linux test suite (gcc-12, all plugins) / Test (ubuntu, gcc-12, all plugins, default config)	53s
test / Run Windows test suite (empty config) / Test (windows, msvc, default plugins, empty config)	1m 24s
test / Run Windows test suite / Test (windows, msvc, default plugins, default config)	2m 26s
	21m 32s

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