selective.exp xfails

[Ben Elliston]

>>>>> "H" == H J Lu <hjl@lucon.org> writes:

  >> ``* Added garbage collection of unused sections, enabled by --gc-sections.
  >> It does require a bit of backend support; currently implemented are
  >> arm-elf, avr-elf, d10v-elf, fr30-elf, i386-elf, m32r-elf, m68k-elf,
  >> mcore-elf, mips-elf, mn10300-elf, ppc-elf, sh-elf, sparc-elf, and v850-elf.
  >> Others will ignore the option.''

  H> I don't believe GC works on ELF/mips. I don't remeber seeing any real
  H> GC code in elf32-mips.c. It is quite tricky due to the MIPS ABI. I
  H> never bother to fix it.

elf32-mips.c:#define elf_backend_can_gc_sections        true

It's working fine on the various mips targets I tried.

Ben