Discard zero address range eh_frame FDEs

These are useless because they can't match any address.  In fact,
worse than useless because the .eh_frame_hdr lookup table matching
addresses to FDEs does not contain information about the FDE range.
The table is sorted by address;  Range is inferred by the address
delta from one entry to the next.  So if a zero address range FDE is
followed by a normal non-zero range FDE for the same address,
everything is good.  However, the qsort could just as easily sort the
FDEs in the other order, in which case the normal FDE would
effectively be seen to have a zero range.

bfd/
	PR 17447
	* elf-bfd.h (struct eh_cie_fde): Comment re NULL u.fde.cie_inf.
	* elf-eh-frame.c (_bfd_elf_parse_eh_frame): Mark zero address
	range FDEs for discarding.
	(vma_compare): Sort on range after address.
	(_bfd_elf_gc_mark_fdes): Test for NULL u.fde.cie_inf.
	(_bfd_elf_discard_section_eh_frame): Likewise.  Write "FDE" in
	error message rather than "fde".
	(_bfd_elf_write_section_eh_frame_hdr): Write "PC" and "FDE" in
	error message.
ld/testsuite/
	* ld-elf/eh1.s: Don't create FDEs with zero address ranges.
	* ld-elf/eh3.s: Likewise.
	* ld-elf/eh1.d, * ld-elf/eh2.d, * ld-elf/eh3.d: Adjust.
	* ld-mips-elf/eh-frame1-n32.d: Warning match update.
	* ld-mips-elf/eh-frame1-n64.d: Likewise.
	* ld-mips-elf/eh-frame2-n32.d: Likewise.
	* ld-mips-elf/eh-frame2-n64.d: Likewise.
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