[RFC][PATCH] tunables: Add elision tunable

[Gabriel F. T. Gomes]

On 12 Sep 2017, Stefan Liebler wrote:

>I've also used a small s390 specific test program to check wether a 
>mutex was elided or not:
>./prog
>Lock was a normal lock!
>
>GLIBC_TUNABLES=glibc.elision.enable=0 ./prog
>Lock was a normal lock!
>
>GLIBC_TUNABLES=glibc.elision.enable=1 ./prog
>Lock was elided via a transaction! (nesting-depth=1)
>
>GLIBC_TUNABLES=glibc.elision.enable=1 ./prog_secure
>Lock was a normal lock!

Would you be willing to share this test program (and your build
configurations)?  I understand that it is s390-specific, but it could help
anyway (at least for my education, it will).