Cchristian it is not about random idea. It is how to write simple
readable and correct autoconf script. Compare my check for functions
(see attached  bootstrap.sh) with you. Also some of macros in you patch
are marked as obsolete.

$ CC=g++ ./bootstrap.sh
...
#define HAVE_SEM_OPEN 1
#define HAVE_SEM_OPEN_XXX 0
#define HAVE_SEM_OPEN_YYY 0
#define HAVE_SEM_TIMEDWAIT 1
...

So you propose check that fail in some cases.