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uclibc: add patches to simplify Thumb handling

This commit adds a number of patches to uClibc that radically
simplifies the Thumb handling. uClibc currently has three options that
you need to toggle on Thumb configurations depending on the specific
ARM CPU being targeted.

However, it turns out that none of those options are necessary:

 - USE_BX can simply be guessed by looking at the ARM core being
   used. The bx instruction is available for all ARM cores >=
   ARMv4T. This is exactly what glibc is doing.

 - USE_LDREXSTREX can also be guessed by looking at the ARM core being
   used: whenever you have Thumb2, ldrex/strex is available.

 - COMPILE_IN_THUMB becomes useless, since all it does is passing
   -mthumb. But just like the uClibc config options to set
   --march=<foo> have been removed a long time ago, there's no need to
   -have an option to pass -mthumb.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>