4.5: half-precision floating point for ARM Cortex A9

[Sandra Loosemore]

I just want to give folks a heads-up on this, to avoid possible duplication of 
effort:

I will be submitting patches to implement half-precision floating point support 
for the ARM Cortex A9 at some point after trunk re-opens for new features. 
Half-precision (16-bit) floating point is a new feature in the IEEE 754-2008 
standard and some of the pieces I've added for C and C++ language support are 
not ARM-specific.  However, since ARM had an existing implementation in their 
own RealView compiler already, we've pretty much copied what they did in terms 
of syntax and semantics.  The main peculiarity is that this is a storage format 
only, not an arithmetic format, so all __fp16 values are promoted to float in 
expressions much the same way that char and short are promoted to int.

I originally made these changes on a 4.3-based toolchain and am just now 
starting to update the patches and clean them up for submission, now that it 
looks like we are getting close to forking 4.4.  Since this is currently a 
background task for me, it'll likely be a week or two before I have anything 
ready to post.

-Sandra