Remove not needed checks and code for VS2015 [VS2013 -> VS2015]

Some pragma warnings are not more needed for VS2015 compilation this
removes them.
Removing some specific code for older version than VS2015.
Forcing build to fail if compiling with VS older than VS2015.

Differential Revision: https://code.wildfiregames.com/D1396
Reviewed by: @Itms
This was SVN commit r23416.

source/third_party/cppformat/format.cpp

@@ -91,9 +91,7 @@ inline int isinfinity(long double x) { return std::isinf(x); }
 
 # pragma warning(push)
 # pragma warning(disable: 4127) // conditional expression is constant
-#if _MSC_VER > 1800
 # pragma warning(disable:4456) // hides previous local declaration
-#endif
 
 inline int getsign(double value) {
   if (value < 0) return 1;

source/third_party/cppformat/format.h

@@ -81,7 +81,7 @@
 // Variadic templates are available in GCC since version 4.4
 // (http://gcc.gnu.org/projects/cxx0x.html) and in Visual C++
 // since version 2013.
-# if defined(_MSC_VER) && _MSC_VER >= 1800
+# if defined(_MSC_VER)
 #  define FMT_USE_VARIADIC_TEMPLATES 1
 # else
 # define FMT_USE_VARIADIC_TEMPLATES \
@@ -95,7 +95,7 @@
 // as the latter doesn't provide std::move.
 # if defined(FMT_GNUC_LIBSTD_VERSION) && FMT_GNUC_LIBSTD_VERSION <= 402
 #  define FMT_USE_RVALUE_REFERENCES 0
-# elif defined(_MSC_VER) && _MSC_VER >= 1600
+# elif defined(_MSC_VER)
 #  define FMT_USE_RVALUE_REFERENCES 1
 # else
 #  define FMT_USE_RVALUE_REFERENCES \

source/third_party/mikktspace/mikktspace.cpp

@@ -7,9 +7,7 @@
 #include "precompiled.h"
 
 #ifdef _MSC_VER
-#if _MSC_VER > 1800
 # pragma warning(disable:4456) // hides previous local declaration
-#endif
 # pragma warning(disable:4189) // local variable is initialized but not referenced
 #endif
 

source/third_party/mikktspace/weldmesh.cpp

@@ -6,10 +6,8 @@
 #include "precompiled.h"
 
 #ifdef _MSC_VER
-#if _MSC_VER > 1800
 # pragma warning(disable:4456) // hides previous local declaration
 #endif
-#endif
 
 /**
  *  Copyright (C) 2011 by Morten S. Mikkelsen

source/third_party/mongoose/mongoose.cpp

@@ -20,14 +20,12 @@
 # pragma warning(disable:4100) // unreferenced formal parameter
 # pragma warning(disable:4245) // signed/unsigned mismatch
 # pragma warning(disable:4505) // unreferenced local function has been removed
-#if _MSC_VER > 1800
 # pragma warning(disable:4365) // signed unsigned mismatch
 # pragma warning(disable:4191) // unsafe conversion
 # pragma warning(disable:4820) // incorrect padding
 # pragma warning(disable:4668) // macro error
 # pragma warning(disable:4710) // function not inlined
 # pragma warning(disable:4711) // selected for automatic inline expansion
-#endif
 # pragma comment(lib, "ws2_32.lib")
 #endif