memcpy overlap: quickly detect, diagnose, work around

[Kevin Kofler]

John Reiser wrote:
> This patch (with .rpms for x86_64 and i686) enables glibc optionally
> to detect, diagnose, and work around overlap in memcpy/mempcpy:
>     http://bitwagon.com/glibc-memlap/glibc-memlap.html
> The option to check is controlled by an environment variable
> MEMCPY_CHECK_ which influences choices made by __init_cpu_features
> and the STT_GNU_IFUNC mechanism for choosing alternate implementations
> at runtime.

This does not work where the memcpy is inlined (which glibc can do in 
several cases).

        Kevin Kofler