[Bug d/88150] Use sections_elf_shared.d on Solaris

[ibuclaw at gdcproject dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88150

--- Comment #1 from Iain Buclaw <ibuclaw at gdcproject dot org> ---
Thanks, I will write up a small documentation of how the sections modules
interacts with runtime - along with compiler support.

As its heavily dependent on compiler and object format, I'll move the
implementation out of the common rt package and over into gcc also.