mstring.c uses strlen() and memcpy() but doesn't #include <string.h>
Created attachment 167838 [details, diff] trivial fix
Thanks for the patch. I'll take this bug myself, since I see there is no gentoo maintainer for this package. I've already sent your fix upstream with a link to this bug, though I'm afraid upstream has ceased development (seems to be no new releases in a long time).
if it's unmaintained upstream, we should just apply the patch in our tree.
Patch committed