[PATCH] D21607: [ELF] - Proccess 'extern' keyword in version scripts.

[Rafael Espíndola via llvm-commits]

> Here is that script file:
> https://github.com/freebsd/freebsd/blob/master/gnu/lib/libsupc%2B%2B/Version.map

It really feels like we should try changing the script. Specially
things like "typeinfo name for ..." where it feels like the matching
depends on the particularities of a human readable output.

It would be even better to not use a script and just create the symbol
with the correct visibility, but that is more work.

Cheers,
Rafael