Automatic way to determine Visual Studio version and hence required library

[MarkRivers]

From Andrew Johnson:

Hi Mark,
On 12/4/18 9:19 AM, Mark Rivers via Tech-talk wrote:
  * On Windows the name of the required FlyCap2 library now depends on what version of Visual Studio 
    is being used.  It is FlyCapture2_v100.lib for VS 2010, FlyCapture2_v120.lib for VS 2013,
    and FlyCapture2_v140.lib for VS 2015.
    I have not yet found a way to have the Makefile automatically detect the VS version, so the Makefiles
    will need to be manually edited if VS 2015 is not being used.
In Base we are using the following to detect VS-2015 or later; the vcvars*.bat scripts from VS-2015 onwards do now set an environment variable with the version:

# option needed for parallel builds with Visual Studio 2015 onward
#
# -FS Force Synchronous PDB Writes
ifneq ($(VisualStudioVersion),)
  OPT_CXXFLAGS_NO += -FS
  OPT_CFLAGS_NO += -FS
endif
For my VS-2017 installation the value is:

C:\epics>echo %VisualStudioVersion%
15.0
I don't have an automatic solution for earlier VS versions though.

- Andrew

This should be used to determine which version of FlyCapture2 to use in the Makefiles.