Fix --gc-sections for C++ MIPS ELF

[Eric Botcazou]

> Non-PIC CIEs for targets like x86_64-linux-gnu also have direct references
> to the personality routines.  I suspect the only reason -Wl,--gc-sections
> -static-libgcc works for them is that libgcc's own CIEs use an indirect
> reference, so the section gets marked that way.

The section is supposed to be always marked, see scripttempl/elf.sc.

-- 
Eric Botcazou