libthr: wrap pdfork(2), same as fork(2).

[kib]

Summary

Without wrapping, rtld services and malloc(3) are not guaranteed to operate correctly in the child.

[markj]

lib/libc/sys/Symbol.map

810

Why not add a _pdfork symbol?

pdfork sorts before pipe.

lib/libc/sys/pdfork.c

41

What's the purpose of this symbol? I note that __fork is not exported by libc.

lib/libthr/thread/thr_fork.c

217

We should just return -1 here I think.

[kib]

lib/libc/sys/Symbol.map

810

There is no need in _pdfork, libc does not use it.

Re-sorted.

lib/libc/sys/pdfork.c

41

This is forgotten line. I planned to use it in libthr but then realized that I do not need it.

lib/libthr/thread/thr_fork.c

217

We need to undo everything we did to prepare for fork. This is mostly theoretical, of course.

[kib]

Remove unused alias, sort symbols in map file.