[Patch]: Fix ld pr11138 FAILures on mips*.

[David Daney]

The pr11138 testcase links an executable with a version script.  On 
mips64-linux the presence of a version script was causing the 
MIPS_RLD_MAP dynamic tag to be populated with a NULL value.  When such 
an executable was run ld.so would try to dereference this and receive 
SIGSEGV, thus killing the process.

The root cause of this is that the mips linker synthesizes a special 
symbol "__RLD_MAP", and then sets MIPS_RLD_MAP to point to it.  When a 
version script is present, this symbol gets versioned along with all the 
rest, and when it is time to take its address, the symbol can no longer 
be found as it has had version information appended to its name.

Since "__RLD_MAP" is really part of the ABI, we want to exclude it from 
symbol versioning.  To this end, I introduced a new symbol flag 
'no_sym_version' to tag this type of symbol.  When the "__RLD_MAP" 
symbol is created, we set this flag.

In _bfd_elf_link_assign_sym_version, we then skip all symbols that have 
'no_sym_version' set, and everything now works.

This problem has also been reported in the wild when linking the firefox 
executable.

Tested on mips64-linux-gnu and x86_64-linux-gnu

Ok to commit?

2011-12-05  David Daney  <david.daney@cavium.com>

	* elf-bfd.h (elf_link_hash_entry): Add no_sym_version field.
	* elflink.c (_bfd_elf_link_assign_sym_version): Don't assign a
	version if no_sym_version is set.
	* elfxx-mips.c (_bfd_mips_elf_create_dynamic_sections): Set
	no_sym_version for "__RLD_MAP".
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