VS2005 tweaks (thanks, Ozkan!).

Fixes Bugzilla #2895.

His notes:

The following trivial changes make SDL2 tree (mostly) compatible with Visual
Studio 2005:

* SDL_stdlib.c: Similar to VS2010 and newer, VS2005 also generates memcpy(),
  (it also generates memset(), see below), so propagate the #if condition to
  cover VS2005.

* SDL_pixels.c (SDL_CalculateGammaRamp): VS2005 generates a memset() call for
  gamma==0 case, so replace the if loop with SDL_memset().

* SDL_windowsvideo.h: Include msctf.h only with VS2008 and newer, otherwise
  include SDL_msctf.h

* SDL_windowskeyboard.c: Adjust the #ifdefs so that SDL_msctf.h inclusion is
  always recognized correctly.

src/stdlib/SDL_stdlib.c

@@ -279,7 +279,8 @@ __declspec(selectany) int _fltused = 1;
 #endif
 
 /* The optimizer on Visual Studio 2010/2012 generates memcpy() calls */
-#if _MSC_VER >= 1600 && defined(_WIN64) && !defined(_DEBUG)
+/* Visual Studio 2005 does it too, and it also generates memset() calls */
+#if (_MSC_VER == 1400 || _MSC_VER >= 1600) && defined(_WIN64) && !defined(_DEBUG)
 #include <intrin.h>
 
 #pragma function(memcpy)

src/video/SDL_pixels.c

@@ -1101,9 +1101,7 @@ SDL_CalculateGammaRamp(float gamma, Uint16 * ramp)
 
     /* 0.0 gamma is all black */
     if (gamma == 0.0f) {
-        for (i = 0; i < 256; ++i) {
-            ramp[i] = 0;
-        }
+        SDL_memset(ramp, 0, 256 * sizeof(Uint16));
         return;
     } else if (gamma == 1.0f) {
         /* 1.0 gamma is identity */

src/video/windows/SDL_windowskeyboard.c

@@ -211,7 +211,12 @@ void IME_Present(SDL_VideoData *videodata)
 
 #else
 
-#ifdef __GNUC__
+#ifdef _SDL_msctf_h
+#define USE_INIT_GUID
+#elif defined(__GNUC__)
+#define USE_INIT_GUID
+#endif
+#ifdef USE_INIT_GUID
 #undef DEFINE_GUID
 #define DEFINE_GUID(n,l,w1,w2,b1,b2,b3,b4,b5,b6,b7,b8) static const GUID n = {l,w1,w2,{b1,b2,b3,b4,b5,b6,b7,b8}}
 DEFINE_GUID(IID_ITfInputProcessorProfileActivationSink,        0x71C6E74E,0x0F28,0x11D8,0xA8,0x2A,0x00,0x06,0x5B,0x84,0x43,0x5C);

src/video/windows/SDL_windowsvideo.h

@@ -27,7 +27,7 @@
 
 #include "../SDL_sysvideo.h"
 
-#if defined(_MSC_VER)
+#if defined(_MSC_VER) && (_MSC_VER >= 1500)
 #include <msctf.h>
 #else
 #include "SDL_msctf.h"