RFH: Symbol versions for __aeabi symbols

[Paolo Carlini]

> This has been done in the past by using port_specific_symbol_files,
> say adding a
> 
> config/cpu/arm/arm-extra.ver
> 
> file with the new symbols in CXXABI_ARM_1.3.
> 
> I would suggest re-using this approach, or some close variant.
> 
> This has the advantage of being a similar approach to the one
> used for the CXXABI_LDBL_1.3 exports used on some arches (powerpc/sparc/s390)
> for long double changes.

Ah! Thanks for reminding this, Benjamin!

Paolo.