libgcc, X86, Darwin: Handle symbols for HF cases.

This reorganises the Darwin symbol vers files to include
the generic ones at the top level; allowing for arch ports
to override (via either exclusion or inclusion as needed).

We add an X86-specific vers file containing the new HF
symbols.  Note that although Darwin does not use ELF-style
symbol versioning - the parser that produces the map can
consume it.  Using the ELF-style description will help us
know at which rev the symbols were introduced.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>

libgcc/ChangeLog:

	* config/i386/t-darwin: Add in a vers file for X86-specific
	symbols.
	* config/t-darwin: Add the generic symbol maps here...
	* config/t-slibgcc-darwin: ... removing from here.
	* config/i386/libgcc-darwin.ver: New file.