tests: Use -fno-strict-aliasing for memtest

There's just no way to do this piece correctly:
    int dummy = 0;
    printf("corrupting our stack...\n");
    *(volatile long long*)&dummy = 0;

Change-Id: If02ff71b3c23c3d8118694f6edba0ecf904baf8a
Signed-off-by: Bernhard Rosenkraenzer <Bernhard.Rosenkranzer@linaro.org>