Well, MorphOS has no certified POSIX, our header doesn't follow "The <stdlib.h> header shall define the symbolic constants and macros as described in <sys wait.h="">" http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/stdlib.h.html
Please take a look at AC_HEADER_SYS_WAIT https://www.gnu.org/software/autoconf/manual/autoconf-2.67/html_node/Particular-Headers.html
Missing WEXITSTATUS macro
Fix bug #928
It works in macOS, seems to be a problem of Windows.
Fixed model confusion and some typos.