getrandom: Fix compilation error in C++ mode on FreeBSD 12

[Bruno Haible]

On FreeBSD 12, in C++ mode, the getrandom() function is declared with C++
linkage. This leads to a compilation error in test-sys_random-c++:

In file included from ../../gltests/test-sys_random-c++.cc:22:
../gllib/sys/random.h:594:19: error: declaration of 'getrandom' has a different 
language linkage
_GL_CXXALIASWARN (getrandom);
                  ^
/usr/include/sys/random.h:160:9: note: previous declaration is here
ssize_t getrandom(void *buf, size_t buflen, unsigned int flags);
        ^

This patch fixes it.


2022-09-02  Bruno Haible  <bruno@clisp.org>

        getrandom: Fix compilation error in C++ mode on FreeBSD 12.
        * lib/sys_random.in.h (getrandom): Enable the C++ alias warning only on
        glibc ≥ 2.25 systems.

diff --git a/lib/sys_random.in.h b/lib/sys_random.in.h
index e730e6139f..c91bcd2cd0 100644
--- a/lib/sys_random.in.h
+++ b/lib/sys_random.in.h
@@ -84,7 +84,9 @@ _GL_FUNCDECL_SYS (getrandom, ssize_t,
 _GL_CXXALIAS_SYS (getrandom, ssize_t,
                   (void *buffer, size_t length, unsigned int flags));
 # endif
+# if __GLIBC__ + (__GLIBC_MINOR__ >= 25) > 2
 _GL_CXXALIASWARN (getrandom);
+# endif
 #elif defined GNULIB_POSIXCHECK
 # undef getrandom
 # if HAVE_RAW_DECL_GETRANDOM