[PATCH, libstdc++] Fix detection of posix_memalig for cross-builds

[Jonathan Wakely]

On 30/11/16 19:00 +0000, Bernd Edlinger wrote:
>Hi,
>
>I noticed that a cross-compiler produces an unusable libstdc++.so
>that contains an unresolved reference to aligned_alloc instead of
>posix_memalign, or whatever is actually available.
>
>Therefore it is impossible to link any C++ programs against the
>libstdc++.so that comes with the cross-compiler.
>
>That happens for instance in the following configuration:
>--target=arm-linux-gnueabihf.
>
>The attached patch adds a link test for the memalign function
>and fixes the cross-build for me.
>
>Is it OK for trunk?

OK.

Presumably we should have this for other cross targets too.