git-compat-util.h: remove superfluous test for __sun__

This 'ifndef' macro is entered only when __sun__ is not defined.  This test
will never fail since it is located inside of the 'else' branch of an 'if'
macro which tests whether __sun__ is defined.  It has had no effect since
the merge at 436f66b.

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-compat-util.h

@@ -57,10 +57,8 @@
 # endif
 #elif !defined(__APPLE__) && !defined(__FreeBSD__)  && !defined(__USLC__) && !defined(_M_UNIX) && !defined(sgi)
 #define _XOPEN_SOURCE 600 /* glibc2 and AIX 5.3L need 500, OpenBSD needs 600 for S_ISLNK() */
-#ifndef __sun__
 #define _XOPEN_SOURCE_EXTENDED 1 /* AIX 5.3L needs this */
 #endif
-#endif
 #define _ALL_SOURCE 1
 #define _GNU_SOURCE 1
 #define _BSD_SOURCE 1