targ-include multilib appears broken

[Shaun Jackman]

The build for each of the multilib directories is including from
arm-elf/newlib/targ-include instead of their specific multilib
targ-include, and the . (dot) multilib appears to be built after the
thumb multilib, so arm-elf/newlib/targ-include doesn't yet exist when
thumb is being built. I hacked around this by copying the targ-include
from thumb to . (dot).

cp -a arm-elf/thumb/newlib/targ-include arm-elf/newlib/targ-include

Cheers,
Shaun