build issues with gnulib

[Bruno Haible]

Hi Martin,

In <https://savannah.gnu.org/bugs/?57406> you wrote:
> I'm running into some other build issues in the gltests subdirectory though,
> in my clang/libc++/ucrt setup

These issues fall in three categories:
  - issues with _GL_CXXALIAS_SYS,
  - issues with _GL_CXXALIASWARN,
  - issues with included C++ header files.

For the first two categories, the fix is very simple, but hard to guess
if you're not familiar with gnulib.

For the third category, the fix may be hard or simple - it depends. In this
case as well, if you write to bug-gnulib, it may save you quite some headaches.

Bruno