Commit 2bf2bf23 exposed a bug on targets that create common sections
other than the standard ELF SHN_COMMON.  If these are output by ld -r,
then their type becomes SHT_PROGBITS unless the target handles them
specially (eg. by elf_backend_special_sections), and if they are
merged into .bss/.sbss by ld -r then that section becomes SHT_PROGBITS.

Worse, if they are output by ld -r, then their size is increased by
bfd_generic_define_common_symbol during final link, which leads to
bogus file contents being copied to output.

For mips, it seems to me that the .scommon section should not be
output for ld -r, but I haven't made that change in this patch.

	PR 24015
	* elf.c (bfd_elf_get_default_section_type): Make common sections
	SHT_NOBITS.
	* linker.c (bfd_generic_define_common_symbol): Clear
	SEC_HAS_CONTENTS.