[clang] Fixed x86 cpuid NSC signature

Summary:
The signature "Geode by NSC" for NSC vendor is wrong.
In lib/Headers/cpuid.h, signature_NSC_edx and signature_NSC_ecx constants are inverted (cpuid signature order is ebx # edx # ecx).

Reviewers: teemperor, rsmith, craig.topper

Reviewed By: teemperor, craig.topper

Subscribers: craig.topper, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D65978

llvm-svn: 368510