Re: sys_un: New module.

[Collin Funk]

Hi Bruno,

The warnings say:

>     ../gllib/string.h:809:20: error: declaration of 'memchr' has a different 
> language linkage
>       809 | _GL_CXXALIASWARN1 (memchr, void *,
>           |                    ^
>     /usr/include/string.h:94:1: note: previous definition is here
>        94 | memchr (void *__s, int __c, size_t __n) __THROW
>           | ^

Initially looking at glibc's string.h on my system I had suspicions of
the following code in string.h:

    /* Tell the caller that we provide correct C++ prototypes.  */
    #if defined __cplusplus && (__GNUC_PREREQ (4, 4) \
                            || __glibc_clang_prereq (3, 5))
    # define __CORRECT_ISO_CPP_STRING_H_PROTO
    #endif
    [...]
    #ifdef __CORRECT_ISO_CPP_STRING_H_PROTO
    extern "C++"
    {
    extern void *memchr (void *__s, int __c, size_t __n)
        __THROW __asm ("memchr") __attribute_pure__ __nonnull ((1));
    extern const void *memchr (const void *__s, int __c, size_t __n)
        __THROW __asm ("memchr") __attribute_pure__ __nonnull ((1));
    [...]

Upon looking further I see that someone else ran into errors like this
using clang++ in 2021 [1]. AFAIK it was never resolved but the archives
split replies by month I think. So maybe I am wrong.

Does this sound reasonable to you? I have attached a patch that should
fix the testdir of all modules while using clang++.

Those _GL_CXXALIASWARN1, etc. macros sort of go over my head so sorry if
I am totally off mark.

Collin

[1] https://lists.gnu.org/archive/html/bug-gnulib/2021-01/msg00206.html

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