qsort_r: Fix compilation error with SunPRO C++ on Solaris 10

[Bruno Haible]

On Solaris 10, with cc and CC as compilers, I get this compilation error:

"../gllib/stdlib.h", line 1406: Error: Cannot return extern "C" 
void(*)(void*,unsigned,unsigned,extern "C" int(*)(const void*,const 
void*,void*),void*) from a function that should return 
void(*)(void*,unsigned,unsigned,int(*)(const void*,const void*,void*),void*).

Apparently this compiler is picky regarding C linkage vs. C++ linkage of
function types. This patch fixes it.


2021-12-24  Bruno Haible  <bruno@clisp.org>

        qsort_r: Fix compilation error with SunPRO C++ on Solaris 10.
        * lib/stdlib.in.h (_gl_qsort_r_compar_fn): New type.
        (qsort_r): Use it.
        * tests/test-stdlib-c++.cc (qsort_r): Don't test with SunPRO C++.

diff --git a/lib/stdlib.in.h b/lib/stdlib.in.h
index 0855112d1..cb99492b3 100644
--- a/lib/stdlib.in.h
+++ b/lib/stdlib.in.h
@@ -828,29 +828,35 @@ _GL_CXXALIASWARN (putenv);
 /* Sort an array of NMEMB elements, starting at address BASE, each element
    occupying SIZE bytes, in ascending order according to the comparison
    function COMPARE.  */
+# ifdef __cplusplus
+extern "C" {
+# endif
+# if !GNULIB_defined_qsort_r_fn_types
+typedef int (*_gl_qsort_r_compar_fn) (void const *, void const *, void *);
+#  define GNULIB_defined_qsort_r_fn_types 1
+# endif
+# ifdef __cplusplus
+}
+# endif
 # if @REPLACE_QSORT_R@
 #  if !(defined __cplusplus && defined GNULIB_NAMESPACE)
 #   undef qsort_r
 #   define qsort_r rpl_qsort_r
 #  endif
 _GL_FUNCDECL_RPL (qsort_r, void, (void *base, size_t nmemb, size_t size,
-                                  int (*compare) (void const *, void const *,
-                                                  void *),
+                                  _gl_qsort_r_compar_fn compare,
                                   void *arg) _GL_ARG_NONNULL ((1, 4)));
 _GL_CXXALIAS_RPL (qsort_r, void, (void *base, size_t nmemb, size_t size,
-                                  int (*compare) (void const *, void const *,
-                                                  void *),
+                                  _gl_qsort_r_compar_fn compare,
                                   void *arg));
 # else
 #  if !@HAVE_QSORT_R@
 _GL_FUNCDECL_SYS (qsort_r, void, (void *base, size_t nmemb, size_t size,
-                                  int (*compare) (void const *, void const *,
-                                                  void *),
+                                  _gl_qsort_r_compar_fn compare,
                                   void *arg) _GL_ARG_NONNULL ((1, 4)));
 #  endif
 _GL_CXXALIAS_SYS (qsort_r, void, (void *base, size_t nmemb, size_t size,
-                                  int (*compare) (void const *, void const *,
-                                                  void *),
+                                  _gl_qsort_r_compar_fn compare,
                                   void *arg));
 # endif
 _GL_CXXALIASWARN (qsort_r);
diff --git a/tests/test-stdlib-c++.cc b/tests/test-stdlib-c++.cc
index 207944528..c16c8a809 100644
--- a/tests/test-stdlib-c++.cc
+++ b/tests/test-stdlib-c++.cc
@@ -114,7 +114,7 @@ SIGNATURE_CHECK (GNULIB_NAMESPACE::ptsname_r, int, (int, 
char *, size_t));
 SIGNATURE_CHECK (GNULIB_NAMESPACE::putenv, int, (char *));
 #endif
 
-#if GNULIB_TEST_QSORT_R
+#if GNULIB_TEST_QSORT_R && !defined __SUNPRO_CC
 SIGNATURE_CHECK (GNULIB_NAMESPACE::qsort_r, void,
                  (void *, size_t, size_t,
                   int (*) (void const *, void const *, void *), void *));