Building and installing base system from source tree in non-default directory

[Yasuhiro KIMURA]

Hello,

Is it possible to checkout base source tree to somewhere other than
/usr/src and to build and install base system by using it?

If it is possible then are some special settings in /etc/src.conf
and/or additional arguments of make(1) required? Or do simply going
to top of source tree and executing 'make buildworld' or other targets
work fine?

Best Regards.

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Yasuhiro KIMURA