[TSan][libdispatch] Fix failing test

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

rdar://49856637

llvm-svn: 358300

compiler-rt/test/tsan/libdispatch/data.c

@@ -4,6 +4,7 @@
 #include <dispatch/dispatch.h>
 
 #include <stdio.h>
+#include <string.h>
 
 long global = 42;