Do not use caller-saved registers for COMDAT functions

Do not use caller-saved registers for COMDAT functions

A reference to a COMDAT function may be resolved to another definition
outside the current translation unit, so it's not eligible for `-fipa-ra`.

In `decl_binds_to_current_def_p()` there is already a check for weak
symbols. This commit checks for COMDAT functions that are not implemented
as weak symbols, for example, on *-*-mingw32.

gcc/ChangeLog:

	PR rtl-optimization/115049
	* varasm.cc (decl_binds_to_current_def_p): Add a check for COMDAT
	declarations too, like weak ones.