Move variable declarations to top of block to fix Visual C++ compilation errors in iovm.
Move variable declarations to top of block to fix Visual C++ compilation errors in SHA1 add-on.
Reorder <math.h> include and fix NAN and isnan defines to fix compilation errors on Visual Studio 2013.
Enable SIMD on x64 for MSVC and use pragma message instead of warning if falling back to emulated SIMD support.