[review] libc: Don't use a custom wrapper macro around __has_include.

[Florian Weimer]

* Florian Weimer:

> Change URL: https://gnutoolchain-gerrit.osci.io/r/c/glibc/+/697
> ......................................................................
>
> libc: Don't use a custom wrapper macro around __has_include.
>
> This causes issues when using clang with -frewrite-includes to e.g., submit the
> translation unit to a distributed compiler.
>
> In my case, I was building Firefox using sccache.
>
> See https://bugs.llvm.org/show_bug.cgi?id=43982 for a reduced test-case since I
> initially thought this was a clang bug.
>
> Apparently doing this is invalid C++ per:
>
>  * http://eel.is/c++draft/cpp.cond#7.sentence-2
>
> (See https://bugs.llvm.org/show_bug.cgi?id=37990)
>
> Signed-off-by: Emilio Cobos Álvarez <emilio@crisal.io>
> Change-Id: Id4b8ee19176a9e4624b533087ba870c418f27e60

Just to be clear here, the patch is from Emilio Cobos Álvarez
<emilio@crisal.io>.  This is correctly recorded in Gerrit, but not
reflected in the email notification.

Florian