Use defined(__sun) instead of defined(sun)

Strict ISO confirming C compilers only define __sun
Reviewed-by: NViktor Dukhovni <openssl-users@dukhovni.org>

RT #4144, MR #1353

crypto/opensslconf.h.in

@@ -137,7 +137,7 @@
    optimization options.  Older Sparc's work better with only UNROLL, but
    there's no way to tell at compile time what it is you're running on */
  
-#if defined( sun )		/* Newer Sparc's */
+#if defined( __sun )		/* Newer Sparc's */
 #  define DES_PTR
 #  define DES_RISC1
 #  define DES_UNROLL

e_os.h

@@ -553,7 +553,7 @@ struct servent *PASCAL getservbyname(const char *, const char *);
 #    include <sys/select.h>
 #   endif
 
-#   if defined(sun)
+#   if defined(__sun)
 #    include <sys/filio.h>
 #   else
 #    ifndef VMS
@@ -595,7 +595,7 @@ struct servent *PASCAL getservbyname(const char *, const char *);
 
 # endif
 
-# if defined(sun) && !defined(__svr4__) && !defined(__SVR4)
+# if defined(__sun) && !defined(__svr4__) && !defined(__SVR4)
   /* include headers first, so our defines don't break it */
 #  include <stdlib.h>
 #  include <string.h>