Don't use native realpath(3) on Solaris

CI shows it does work on Solaris 11, but does not work on Solaris
10.  However, until I figure out a good way to differentiate
between Solaris 10 and 11, this should get CI passing on both.

file.c

@@ -146,6 +146,11 @@ int flock(int, int);
 #  define UTIME_EINVAL
 #endif
 
+/* Solaris 10 realpath(3) doesn't support File.realpath */
+#if defined HAVE_REALPATH && defined __sun && defined __SVR4
+#undef HAVE_REALPATH
+#endif
+
 #ifdef HAVE_REALPATH
 #include <limits.h>
 #include <stdlib.h>