string: Fix compilation error in C++ mode on AIX 7.2 with xlclang

[Bruno Haible]

Another compilation error with xlclang on AIX 7.2 is this one:

depbase=`echo test-string-c++.o | sed 's|[^/]*$|.deps/&|;s|\.o$||'`;\
xlclang++ -qthreaded -qtls -DHAVE_CONFIG_H -DEXEEXT=\"\" -I. -I../../gltests 
-I..  -DGNULIB_STRICT_CHECKING=1 -DIN_GNULIB_TESTS=1 -I. -I../../gltests -I.. 
-I../../gltests/.. -I../gllib -I../../gltests/../gllib 
-I/home/haible/prefix32/include -D_THREAD_SAFE  -Wno-error -g -O2 -MT 
test-string-c++.o -MD -MP -MF $depbase.Tpo -c -o test-string-c++.o 
../../gltests/test-string-c++.cc &&\
mv -f $depbase.Tpo $depbase.Po
In file included from ../../gltests/test-string-c++.cc:22:
../gllib/string.h:1453:19: error: use of undeclared identifier 'mbslen'; did 
you mean 'gnulib::mbslen'?
_GL_CXXALIASWARN (mbslen);
                  ^
../gllib/string.h:1446:19: note: 'gnulib::mbslen' declared here
_GL_CXXALIAS_RPL (mbslen, size_t, (const char *string));
                  ^
1 error generated.
Error while processing ../../gltests/test-string-c++.cc.
Makefile:23408: recipe for target 'test-string-c++.o' failed
gmake[4]: *** [test-string-c++.o] Error 1

Fixed through this patch.


2022-09-10  Bruno Haible  <bruno@clisp.org>

        string: Fix compilation error in C++ mode on AIX 7.2 with xlclang.
        * lib/string.in.h (mbslen): Enable the C++ alias warning only on glibc
        systems.

diff --git a/lib/string.in.h b/lib/string.in.h
index 3996da9fcb..e56f6db0c9 100644
--- a/lib/string.in.h
+++ b/lib/string.in.h
@@ -943,7 +943,9 @@ _GL_FUNCDECL_SYS (mbslen, size_t, (const char *string)
                                   _GL_ARG_NONNULL ((1)));
 _GL_CXXALIAS_SYS (mbslen, size_t, (const char *string));
 # endif
+# if __GLIBC__ >= 2
 _GL_CXXALIASWARN (mbslen);
+# endif
 #endif
 
 #if @GNULIB_MBSNLEN@