[X86] Change getHostCPUName fallback code to not select 'x86-64' for unknown CPUs in family 6 that has 64-bit support but not any newer SSE features. Use 'core2' instead

We know that's the earliest CPU with 64-bit support. x86-64 has taken on a role of representing a more modern 64-bit CPU so we probably shouldn't be using that when we can't identify things.

llvm-svn: 317229
diff --git a/llvm/lib/Support/Host.cpp b/llvm/lib/Support/Host.cpp
index d8fb3e1..7fbe9ad 100644
--- a/llvm/lib/Support/Host.cpp
+++ b/llvm/lib/Support/Host.cpp
@@ -794,8 +794,13 @@
         break;
       }
       if (Features2 & (1 << (FEATURE_EM64T - 32))) {
-        *Type = INTEL_X86_64;
-        break; // x86-64
+        *Type = INTEL_CORE2; // "core2"
+        *Subtype = INTEL_CORE2_65;
+        break;
+      }
+      if (Features & (1 << FEATURE_SSE3)) {
+        *Type = INTEL_CORE_DUO;
+        break;
       }
       if (Features & (1 << FEATURE_SSE2)) {
         *Type = INTEL_PENTIUM_M;