[DynInst_API:] Commit: Visual Studio 2015 Compatibility

[Allison Morris <amorris5@xxxxxxxx>]

Hi all, this commit makes some changes necessary for building Dyninst

on VS 2015. Dyninst should still build on older versions.

+C99 Support:

Older versions of Microsoft's compiler lack support for some C99

functions, such as snprintf. This commit removes Windows-only macros

on VS 2015 builds that were used to provide snprintf. These macros

are still intact for builds using older versions of MSVC.

+Initializer List Support:

Some of DataflowAPI used Boost libraries in Windows builds to make up

for MSVC's lack of initializer list support. Our initializer list code

is now used on VS 2015+ builds, while the Boost code continues to be

used in older MSVC builds.

Best,

Alli