More Solaris additions.

Scanning through the sources I found some places where declarations for Solaris
are missing. This is not complete!
(cherry picked from commit f6b012b5f7ca155bdd818ee66bd87f8846553a58)

Conflicts:
	src/core/sys/posix/stdio.d
Add headers for link time ELF declarations on Solaris.

These header files deal with ELF structures at link time.

This is a backport of https://github.com/D-Programming-Language/druntime/pull/1052