This is not a search and replace of __MING32__ with _WIN32.
There are places where __MINGW32__ is still used and all changes are
tested with MSVC 2019 compiler. Although, this commit alone will not work
on MSVC because there are plenty of other things to be done which are
seperated into multiple PR. PR OSGeo#289 is the one that "works" on MSVC and
unix as well. But that contains too many changes which shouldn't in a single
PR. Even though this PR alone won't compile GRASS GIS on MSVC, it sure will
not break existing compilers which I think is very important.

Complete support for MSVC will be ready after 2/3 PRs

OSGeo#289

static int initialized is not working for MSVC
and must export this with __declspec so that it appears in a DLL
correctly. This change has been tested on Ubuntu and MSVC 2019 and
is working as expected.

Below is a code from filldepr.cpp which throws error on msvc compiler
function has G_fatal_error() so it is 'normal' to have no return type.
But MSVC complains that function's return type is elevation_type*
and does not return anything.

elevation_type*
ext_fill_depression(AMI_STREAM<boundaryType> *boundaryStr,
			 cclabel_type maxWatersheds) {
  G_fatal_error(_("Fill_depressions do not fit in memory. Not implemented yet"));
}

The MSVC compiler only supports C90, it does not support C99
and variable length arrays are a feature of C99.

g.list uses regex.h which is not available on MSVC.
This PR fixes g.list by using pcre library on windows
and use regex.h on other platforms.

This is Work in progress. Need to test the functionality of pcre v. regex