Call for testing: wip/simde

[Jason Bacon <jtocino%gmx.com@localhost>]

I just added wip/simde, a header-only library allowing x86-style SIMD
intrinsics to be used on other platforms.  This eases porting of many
applications containing x86-specific optimizations.

wip/hisat2 is a consumer and compiles correctly on amd64.

Anyone potentially interested in simde on arm, powerpc, or other
platforms can try it out by simply attempting a wip/hisat2 build.
Please let me know if any problems are encountered.