error: conflicting types for 'strmode'
I don't know whether building libbsd on macOS is expected to be useful, since macOS is already based on BSD, but in case this is meant to work, it doesn't; here's the error I get building libbsd 0.9.1 on macOS High Sierra:
In file included from arc4random.c:32:
In file included from ../include/bsd/string.h:28:
In file included from /usr/include/string.h:180:
In file included from /usr/include/strings.h:92:
../include/bsd/string.h:47:6: error: conflicting types for 'strmode'
void strmode(mode_t mode, char *str);
^
/usr/include/string.h:164:7: note: previous declaration is here
void strmode(int __mode, char *__bp);
^
1 error generated.