[patch] Remove NO_IMPLICIT_EXTERN_C target macro

[Hans-Peter Nilsson]

On Mon, 18 Jun 2012, Steven Bosscher wrote:
> The attached patch removes NO_IMPLICIT_EXTERN_C, and replaces its sole
> user with IMPLICIT_EXTERN_C to avoid the double negations (#ifndef
> NO_IMPLICIT_EXTERN_C, etc.).
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu. OK for trunk?

I saw it wasn't part of this patch so: when and if this
eventually gets in, please don't forget to poison it, see
system.h.

brgds, H-P