Errors cross-compiling gdbserver with glibc-2.34

[Florian Weimer]

* Chris Packham via Libc-help:

> I'm looking at updating crosstool-ng to add glibc-2.34. I can generate a 
> toolchain fine but when I try to build gdbserver (which can be enabled 
> as part of the crosstool-ng build) I get some odd gnulib build errors.
>
> https://github.com/crosstool-ng/crosstool-ng/pull/1570#issuecomment-893784531
>
> I can disable building gdbserver as part of crosstool-ng and 
> successfully generate a toolchain. But when I use that toolchain to 
> manually build gdbserver I get the same error (included below as it has 
> a bit more useful output than on the link above).
>
>    CXX    amd64-linux-siginfo.o
> In file included from 
> /home/ctng/x-tools/x86_64-unknown-linux-gnu/x86_64-unknown-linux-gnu/sysroot/usr/include/bits/sigstksz.h:24,
>                   from 
> /home/ctng/x-tools/x86_64-unknown-linux-gnu/x86_64-unknown-linux-gnu/sysroot/usr/include/signal.h:328,
>                   from build-gnulib-gdbserver/import/signal.h:52,
>                   from 
> ../../../gdb-9.2/gdb/gdbserver/../nat/amd64-linux-siginfo.c:20:
> build-gnulib-gdbserver/import/unistd.h:135:3: error: #error "Please 
> include config.h first."

gnulib apparently overrides <unistd.h> with an incompatible header.
There is nothing that glibc can do about this.

Thanks,
Florian