Darwin: Fix a compiler warning

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13319 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/coregrind/m_syswrap/syswrap-darwin.c b/coregrind/m_syswrap/syswrap-darwin.c
index 2e6852e..b0b1583 100644
--- a/coregrind/m_syswrap/syswrap-darwin.c
+++ b/coregrind/m_syswrap/syswrap-darwin.c
@@ -7747,6 +7747,7 @@
 }
 
 
+#if DARWIN_VERS >= DARWIN_10_7
 /* ---------------------------------------------------------------------
    Added for OSX 10.7 (Lion)
    ------------------------------------------------------------------ */
@@ -7761,6 +7762,7 @@
 {
    POST_MEM_WRITE(ARG1, ARG2);
 }
+#endif
 
 PRE(psynch_mutexwait)
 {