[R-SIG-Win] Default mtune for R windows

[Avraham Adler]

I put in a bug request for this over a year ago and it went nowhere.
Nobody is using a core2 on Windows anymore. GCC itself has been
suggesting for a very long time to use '-mtune=generic'. Their
language on 4.9.3. is:

‘generic’ Produce code optimized for the most common IA32/AMD64/EM64T
processors. If youknow the CPU on which your code will run, then you
should use the corresponding -mtune or -march option instead of
-mtune=generic. But, if you do not know exactly what CPU users of your
application will have, then you should use this option.

As new processors are deployed in the marketplace, the behavior of
this option will change. Therefore, if you upgrade to a newer version
of GCC, code generation controlled by this option will change to
reflect the processors that are most common at the time that version
of GCC is released.


How difficult is it to change that line in Mkrules.dist/Mkrules.rules?

Avi