Make VG_(dup2) compile on AIX.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@8693 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/coregrind/m_libcfile.c b/coregrind/m_libcfile.c
index 1236d7e..79e2700 100644
--- a/coregrind/m_libcfile.c
+++ b/coregrind/m_libcfile.c
@@ -262,7 +262,13 @@
 
 SysRes VG_(dup2) ( Int oldfd, Int newfd )
 {
+#  if defined(VGO_linux)
    return VG_(do_syscall2)(__NR_dup2, oldfd, newfd);
+#  elif defined(VGO_aix5)
+   I_die_here;
+#  else
+#    error Unknown OS
+#  endif
 }
 
 /* Returns -1 on error. */