[X86] Add 'fxsr' feature to -march=pentium2 to match X86.td and gcc.

Author: topperc

clang/lib/Basic/Targets/X86.cpp

@@ -246,10 +246,11 @@ bool X86TargetInfo::initFeatureMap(
   case CK_Pentium3:
   case CK_C3_2:
     setFeatureEnabledImpl(Features, "sse", true);
+    LLVM_FALLTHROUGH;
+  case CK_Pentium2:
     setFeatureEnabledImpl(Features, "fxsr", true);
     LLVM_FALLTHROUGH;
   case CK_PentiumMMX:
-  case CK_Pentium2:
   case CK_K6:
   case CK_WinChipC6:
     setFeatureEnabledImpl(Features, "mmx", true);

clang/test/Preprocessor/predefined-arch-macros.c

@@ -184,6 +184,7 @@
 // RUN: %clang -march=pentium2 -m32 -E -dM %s -o - 2>&1 \
 // RUN:     -target i386-unknown-linux \
 // RUN:   | FileCheck -match-full-lines %s -check-prefix=CHECK_PENTIUM2_M32
+// CHECK_PENTIUM2_M32: #define __FXSR__ 1
 // CHECK_PENTIUM2_M32: #define __MMX__ 1
 // CHECK_PENTIUM2_M32: #define __i386 1
 // CHECK_PENTIUM2_M32: #define __i386__ 1