Microsoft Visual Studio 2015 release candidate. This bundle contains
msvc-14.0 for which `_MSC_VER` has the value 1900.

(1) Patches to byterun/floats.c

(a)
  #if defined (_MSC_VER)
  #  include <float.h>
  #  if(MSC_VER < 1900)
  #    define isnan _isnan
  #    define isfinite _finite
  #  endif/*(MSC_VER <= 1900)*/
  #endif /*defined(_MSC_VER)*/

(b)
  void caml_init_ieee_floats(void)
  {
    ...
  #if defined(_MSC_VER) &&_MSC_VER < 1900
    _set_output_format(_TWO_DIGIT_EXPONENT);
  #endif/*defined(_MSC_VER) &&_MSC_VER < 1900*/
  }

(2) Patch to byterun/misc.h

  /* snprintf emulation for Win32 */

  #if defined(_WIN32) && defined(_MSC_VER) && _MSC_VER < 1900
  extern int caml_snprintf(char * buf, size_t size, const char * format,
...);
  #  define snprintf caml_snprintf
  #endif /*defined (_WIN32) && defined (_MSC_VER)&& _MSC_VER < 1900 */

(3) Rebuild flexdll objects with msvc-14.0 (in my case I am interested only
in the 64-bit variants)

  cl.exe /nologo /MD -D_CRT_SECURE_NO_DEPRECATE /GS- /DMSVC  -c
/Fo"flexdll_msvc64.obj" flexdll.c
  cl.exe /nologo /MD -D_CRT_SECURE_NO_DEPRECATE /GS- /DMSVC -c
/Fo"flexdll_initer_msvc64.obj" flexdll_initer.c

(4) Patches to config/Makefile.msvc64 (refer
http://blogs.msdn.com/b/vcblog/archive/2015/03/03/introducing-the-universal-crt.aspx
):

  EXTRALIBS=legacy_stdio_wide_specifiers.lib legacy_stdio_definitions.lib
vcruntime.lib ucrt.lib

​(5) Build the system

        make -f Makefile.nt world
        make -f Makefile.nt bootstrap
        make -f Makefile.nt opt
        make -f Makefile.nt opt.opt
        make -f Makefile.nt install
​
-- 
Shayne Fletcher