Warning fix for gcc/clang

As I build my project with -Wall -Werror this was a blocking error.
Please note that although the fix was not hard to write, there might be subtle errors I didn't spot. I don't think code in death_handler.cc can be multithreaded, so there is no check for concurrent access to the allocators. Please give it a good look before merging.
Source: http://stackoverflow.com/questions/17803456/an-alternative-for-the-deprecated-malloc-hook-functionality-of-glibc