The two versions in the tree requires some patches to build with musl ; respectively applied upstream in next releases, but there is currently no official release working.
With the USE flags set to -nfs, watchdog fails to build due to an include of rpc/types.h, which doesn't exist in sys-libs/musl. There is no problem with the USE flag nfs, because it appends a dependency to net-libs/libtirpc which provides this file. Upstream patch for both 5.14 and 5.15: https://sourceforge.net/p/watchdog/patches/11/
Upstream patch fixing musl build for 5.14: https://sourceforge.net/p/watchdog/patches/9/
Upstream patch fixing musl build for 5.15: https://sourceforge.net/p/watchdog/patches/10/
Since upstream has accepted these, we can backport them.
(In reply to Anthony Basile from comment #1)
> Since upstream has accepted these, we can backport them.
To be clear, we should backport them into the tree, not the overlay.