Include string.h for strcmp.

Change-Id: I57a6505446e63567b0be8496cf1f0d9326e930f7
diff --git a/demangle/Demangler.cpp b/demangle/Demangler.cpp
index 7a3aa81..7bae356 100644
--- a/demangle/Demangler.cpp
+++ b/demangle/Demangler.cpp
@@ -15,6 +15,7 @@
  */
 
 #include <assert.h>
+#include <string.h>
 
 #include <cctype>
 #include <stack>