add missing #include.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51227 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/llvm/System/Path.h b/include/llvm/System/Path.h
index 00e4ea3..2266349 100644
--- a/include/llvm/System/Path.h
+++ b/include/llvm/System/Path.h
@@ -19,6 +19,7 @@
 #include <string>
 #include <vector>
 #include <iosfwd>
+#include <cstring>
 
 namespace llvm {
 namespace sys {