Add the support for Windows

[arttet]

Failed to build on Windows using MinGW.

For example,

• '_SC_PAGESIZE' undeclared in fy-emit.c:1946:22
• There's no alloca.h in Windows

[pantoniou]

Will be addressed by using an additiional meson build system. Getting automake to work on windows is not going to work.

[mseelye]

I was able to build this, and build and run the examples on Windows in an MSys2/Mingw64 environment.

[hapejot]

I would like to see the library to be native compilable under Microsoft C, so there are no dependencies on MSys2 and Mingw64 libraries. But in order to compile this under MS C a huge amount of GNU dependencies need to be changed. And I am not sure if this is an easy task. Since most of the macros use GNU compiler specialies. The build system is not a big deal in my opinion.

Am I the only one interested in a plain windows dll without further dependencies?

[Enjection]

Just built and run some examples under windows with reduced perf and functionality:

• disabled fy-tool
• commented mmap-related functionality
• commented termios related things (probably slightly affects output in diag)
• some calls to alloca replace with malloc
• others with _alloca

Not sure will I contribute it or not soon, because I still need to run tests properly and make my changes readable