[TSan][libdispatch] Fix failing test

The ThreadSanitizer-x86_64-iossim configuration (different SDK) seems to
require an additional #include.

rdar://49856637

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@358300 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/tsan/libdispatch/data.c b/test/tsan/libdispatch/data.c
index bb3aadc..70c503b 100644
--- a/test/tsan/libdispatch/data.c
+++ b/test/tsan/libdispatch/data.c
@@ -4,6 +4,7 @@
 #include <dispatch/dispatch.h>
 
 #include <stdio.h>
+#include <string.h>
 
 long global = 42;