Enable half2float() on windows.

[ADodds]

Summary

This function was disabled for the windows build by Virgil in part of this patch:
http://llvm.org/klaus/lldb/commit/fdf8273428eab9e111ce6b319a9bcf5547ffb5b1/

I have tested this code on VS2013 (Update4) and VS2015 and it builds ok.
I dont want to enable this and break anyones build however.

Is anyone using an older version of VisualStudio (that perhaps doesnt support this function)?

[zturner]

This should be fine on any version of MSVC. Not sure why it was disabled
for MSVC to begin with. ldexpf() was new with VS 2010, but the last time a
compiler older than VS 2010 was supported was a really long time ago.

In any case, VS 2013 is the minimum required version now, and VS 2015 will
be the minimum required version soon. So lgtm.

[ADodds]

If there are no objections, are you happy to accept this?

[zturner]

Yea, sorry. In the future if someone says "lgtm" that's as good as hitting the accept button in phabricator.

lldb/trunk/source/Core/DataExtractor.cpp

 //===-- DataExtractor.cpp ---------------------------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include <assert.h>
 #include <stddef.h>
 
 #include <bitset>
 #include <limits>
 #include <sstream>
 #include <string>
+#include <math.h>
 
 #include "clang/AST/ASTContext.h"
 
 #include "llvm/ADT/APFloat.h"
 #include "llvm/ADT/APInt.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/Support/MathExtras.h"
if (GetAPInt (data, &offset, byte_size, apint))
             case 10:
                 break;
         }
         s->Write(apint_str.c_str(), apint_str.size());
     }
     return offset;
 }
 
-static float half2float (uint16_t half)
+static float
+half2float (uint16_t half)
 {
-#ifdef _MSC_VER
-    llvm_unreachable("half2float not implemented for MSVC");
-#else
-    union{ float       f; uint32_t    u;}u;
+    union { float f; uint32_t u; } u;
     int32_t v = (int16_t) half;
-    
-    if( 0 == (v & 0x7c00))
+    if (0 == (v & 0x7c00))
     {
         u.u = v & 0x80007FFFU;
         return u.f * ldexpf(1, 125);
     }
-    
     v <<= 13;
     u.u = v | 0x70000000U;
     return u.f * ldexpf(1, -112);
-#endif
 }
 
 lldb::offset_t
 DataExtractor::Dump (Stream *s,
                      offset_t start_offset,
                      lldb::Format item_format,
                      size_t item_byte_size,
                      size_t item_count,