demangle: fix missing include of stdlib header (#89)

Signed-off-by: Martin Olivier <martin.olivier@live.fr>

Author: martin-olivier

src/demangle.cpp

@@ -54,6 +54,7 @@ std::string demangle_symbol(const char *symbol) {
 #else /************************   gcc, clang, MinGW   ************************/
 
 #include <cxxabi.h>
+#include <stdlib.h>
 
 std::string demangle_symbol(const char *symbol) {
     std::string result;