varasm: Handle private COMDAT function symbol reference in readonly data section [PR113617]

If default_elf_select_rtx_section is called to put a reference to some
local symbol defined in a comdat section into memory, which happens more often
since the r14-4944 RA change, linking might fail.
default_elf_select_rtx_section puts such constants into .data.rel.ro.local
etc. sections and if linker chooses comdat sections from some other TU
and discards the one to which a relocation in .data.rel.ro.local remains,
linker diagnoses error.  References to private comdat symbols can only appear
from functions or data objects in the same comdat group, so the following
patch arranges using .data.rel.ro.local.pool.<comdat_name> and similar sections.

2024-02-26  Jakub Jelinek  <jakub@redhat.com>
	    H.J. Lu  <hjl.tools@gmail.com>

	PR rtl-optimization/113617
	* varasm.cc (default_elf_select_rtx_section): For
	references to private symbols in comdat sections
	use .data.relro.local.pool.<comdat>, .data.relro.pool.<comdat>
	or .rodata.<comdat> comdat sections.

	* g++.dg/other/pr113617.C: New test.
	* g++.dg/other/pr113617.h: New test.
	* g++.dg/other/pr113617-aux.cc: New test.