arch/arm: OABI is no more, switch to only EABI

Well, leave the prompt as an OBSOLETE thing, scheduled to
be removed soon.

As an indication OABI lives its last days, gcc-4.8 will no
longer recognise non-EABI targets.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

 # windows config options

 ## depends on ARCH_x86

 ##

 ## select WINDOWS

 ##

 ## help Build a toolchain targeting systems running Windows as host