CPU-specific builds

[Ben Woodcroft <b.woodcroft@uq.edu.au>]

Hi,

Currently, we build a single set of x86_64 packages assuming SSE but not 
SSE2 instructions, but sometimes it would be nice to use more recent 
instructions like AVX. So I'm wondering if there is some way to specify 
a system more specific than 'X86_64'? I tried simply adding 
'--with-arch=haswell' as a configure argument in gcc-4.9 so that flag 
became the default for gcc usage and saw some performance improvements, 
though I did have to disable tests in gnutls.

Hardcoding that configure flag is definitely less than ideal, I'm 
wondering if there is some better way that would enable us to share 
package updates and even substitutes for these systems? My initial 
thought is extending the triplet 'x86_64-unknown-linux-gnu' somehow, but 
I suspect others have better ideas?

Thanks, ben.