glibc: enable stackprotection hardening

Enables previously manually disabled stackprotector and stackguard
randomization.

From https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=511811:

    If glibc is built with the --enable-stackguard-randomization option,
    each application gets a random canary value (at runtime) from /dev/urandom.
    If --enable-stackguard-randomization is absent, applications get a static
    canary value of "0xff0a0000". This is very unfortunate, because the
    attacker may be able to bypass the stack protection mechanism, by placing
    those 4 bytes in the canary word, before the actual canary check is
    performed (for example in memcpy-based buffer overflows).