[oe] Making thumb builds easier in OE

[Koen Kooi]

Hi,

I noticed that Phil fixed thumb interworking in glibc for armv4t which 
spurred me to do this:

arm tune files: include tune-thumb by default
* it defaults to non-thumb, so no functional change

So people can now set ARM_INSTRUCTION_SET = "thumb" and resulting ARM 
builds will be in thumb mode.

This does raise a few issues:

  1) How can we handle thumb2? I only changed the arm9 and arm11 tune 
files, how should we do the arm1176 and cortex ones?

  2) Since thumb packages are compatible with non-thumb ones we don't 
really need a seperate arch, but keeping them same feels wrong and is a 
QA nightmare.

for 2) my first thought was to add '-thumb' to the archs, like angstrom 
adds '-oabi' for strongarm packages.

I'm not really interested in a discussion whether thumb(2) is worth it, 
I just want to solve the build- and distro side of it.

Thought suggestions?

regards,

Koen