isnan: Ensure it is a macro.

* lib/math.in.h (isnan): Define as a macro if not already a macro.
* doc/posix-functions/isnan.texi: Mention problem on IRIX, OSF/1,
Solaris.

1 files changed, 4 insertions, 0 deletions

diff --git a/lib/math.in.h b/lib/math.in.h
index 4fbed08d67..0f78264553 100644
--- a/lib/math.in.h
+++ b/lib/math.in.h
@@ -680,6 +680,10 @@ _GL_EXTERN_C int rpl_isnanl (long double x);
     sizeof (x) == sizeof (double) ? gl_isnan_d (x) : \
     gl_isnan_f (x))
 # endif
+/* Ensure isnan is a macro.  */
+# ifndef isnan
+#  define isnan isnan
+# endif
 #elif defined GNULIB_POSIXCHECK
 # if defined isnan
 _GL_WARN_REAL_FLOATING_DECL (isnan);