ninjabackend.py: Implement `link_whole:` for pre-VS2015
ninjabackend.py: Implement `link_whole:` for pre-VS2015

...Update 2, to be exact, since the Visual Studio linker only gained the
`/WHOLEARCHIVE:` feature since Visual Studio 2015 Update 2.

This checks whether we have the corresponding `cl.exe` which is
versioned at or after Visual Studio 2015 Update 2 before we try to apply
the `/WHOLEARCHIVE:xxx` linker flag.  If we aren't, use built-in methods
in Meson to grab the object files of the dependent static lib's, along
with the objects that were `link_whole:`'ed into them, and feed this
list into the linker instead.

This would make `link_whole:` work on Visual Studio 2015 Update 1 and
earlier, including previous Visual Studio versions.

mesonbuild/meson,pexip/meson,pexip/meson,mesonbuild/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,pexip/meson,jpakkane/meson,jpakkane/meson,mesonbuild/meson,jpakkane/meson,mesonbuild/meson,pexip/meson,jpakkane/meson,jpakkane/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,jpakkane/meson,pexip/meson,mesonbuild/meson,jpakkane/meson,pexip/meson,pexip/meson,jpakkane/meson,jpakkane/meson