libc-abis: Define ABSOLUTE ABI [BZ #19818][BZ #23307]

libc-abis: Define ABSOLUTE ABI [BZ #19818][BZ #23307]

Define a new ABSOLUTE ABI for static linker's use with EI_ABIVERSION
where correct absolute (SHN_ABS) symbol run-time load semantics is
required.  This way it can be ensured at static link time that a program
or DSO will not suffer from previous semantics where absolute symbols
were relocated by the base address, or symbols whose `st_value' is zero
silently ignored leading to a confusing "undefined symbol" error message
at load time, and instead "ELF file ABI version invalid" is printed with
old dynamic loaders, making it clear that there is an ABI version
incompatibility.

	[BZ #19818]
	[BZ #23307]
	* libc-abis (ABSOLUTE): New ABI.
	* sysdeps/unix/sysv/linux/mips/libc-abis (ABSOLUTE): New ABI.
	* NEWS: Mention the new ABI.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>