This updates the __init__ constructor method of CCompiler so that distutils
can be used, with some environment or user-supplied options to create the
compiler instance that is appropriate with the platform that the giscanner
scripts are being run on, and sets some specific environment for the
compilers as necessary.  This also adds a check_is_msvc() method that will
progressively replace calls in the other giscanner scripts that attempt to
check for CC=cl (or so), where a part of which is done in this patch.  This
is done for dumper.py as well as it needs to be updated in this patch to
use the updated ccompiler.py which uses distutils to initiate the compiler
instance.

Also, as we have been using the --library option on Windows to pass in the
library (not DLL) to deduce the correct DLL to link to in the introspection
files for some time, we no longer need to make a copy of the library (.lib)
to introspect that matches the <namespace>-<namespace_version>.lib
convention, but use the libraries that were passed in with --library
directly, so that we can link the dumper program during the introspection
build.

Please note that this also partially reverts commit c9cfa2b5 as the
distutils items are clearly needed for these to work.

https://bugzilla.gnome.org/show_bug.cgi?id=728313