i#1673 large Mac apps: replace bzero and _platform_bzero
i#1673 large Mac apps: replace bzero and _platform_bzero

Adds replacement of bzero and _platform_bzero.  The replacement routine
simply calls memset.

Review-URL: https://codereview.appspot.com/268730043

LohithBlaze/drmemory,code4bones/drmemory,LohithBlaze/drmemory,code4bones/drmemory,code4bones/drmemory,code4bones/drmemory,LohithBlaze/drmemory,LohithBlaze/drmemory,LohithBlaze/drmemory,code4bones/drmemory