[test-suite] PGO and reference input support for SPEC

Description

[test-suite] PGO and reference input support for SPEC

Summary:
LNT has this underused feature that lets you defined tests in python. I used
this feature to implement PGO and reference input support for SPEC2000_int,
SPEC2006_{int,fp}.

The module currently uses configure/make to build the benchmarks (this can
obviously be changed to cmake in the long run). The tests are then directly
run from python and then the output is verified.

This new method is off by default. You need to invoke lnt runtest nt with
--spec-with-ref to enable it. Also PGO is supported with --spec-with-pgo.

I still need to add RunSafely and remote support. Also some tests depend on
endianness and I only added little endian support at this point.

Reviewers: cmatthews

Subscribers: llvm-commits, MatzeB

Differential Revision: http://reviews.llvm.org/D14734

Details