[X86] Add slow div64 tuning flag to Nehalem target (#91129)

This appears to have been missed because later cpus don't inherit from Nehalem tuning much.

Noticed while cleaning up for #90985

Author: RKSimon

llvm/lib/Target/X86/X86.td

@@ -873,6 +873,7 @@ def ProcessorFeatures {
   // Nehalem
   list<SubtargetFeature> NHMFeatures = X86_64V2Features;
   list<SubtargetFeature> NHMTuning = [TuningMacroFusion,
+                                      TuningSlowDivide64,
                                       TuningInsertVZEROUPPER,
                                       TuningNoDomainDelayMov];
 

llvm/test/CodeGen/X86/bypass-slow-division-64.ll

@@ -7,7 +7,7 @@
 ; RUN: llc < %s -mtriple=x86_64-- -mcpu=x86-64-v3       | FileCheck %s --check-prefixes=CHECK,SLOW-DIVQ
 ; RUN: llc < %s -mtriple=x86_64-- -mcpu=x86-64-v4       | FileCheck %s --check-prefixes=CHECK,SLOW-DIVQ
 ; Intel
-; RUN: llc < %s -mtriple=x86_64-- -mcpu=nehalem         | FileCheck %s --check-prefixes=CHECK,FAST-DIVQ
+; RUN: llc < %s -mtriple=x86_64-- -mcpu=nehalem         | FileCheck %s --check-prefixes=CHECK,SLOW-DIVQ
 ; RUN: llc < %s -mtriple=x86_64-- -mcpu=sandybridge     | FileCheck %s --check-prefixes=CHECK,SLOW-DIVQ
 ; RUN: llc < %s -mtriple=x86_64-- -mcpu=haswell         | FileCheck %s --check-prefixes=CHECK,SLOW-DIVQ
 ; RUN: llc < %s -mtriple=x86_64-- -mcpu=skylake         | FileCheck %s --check-prefixes=CHECK,SLOW-DIVQ