Windows fixes (ggml-org#890)

Mostly for msys2 and mingw64 builds, which are different from each other
and different from standard Visual Studio builds.  Isn't Windows fun?

- Define _GNU_SOURCE in more files (it's already used in ggml.c for
  Linux's sake).

- Don't use PrefetchVirtualMemory if not building for Windows 8 or later
  (mingw64 doesn't by default).  But warn the user about this situation
  since it's probably not intended.

- Check for NOMINMAX already being defined, which it is on mingw64.

- Actually use the `increment` variable (bug in my `pizza` PR).

- Suppress unused variable warnings in the fake pthread_create and
  pthread_join implementations for Windows.

- (not Windows-related) Remove mention of `asprintf` from comment;
  `asprintf` is no longer used.

Fixes ggml-org#871.

Fix whitespace, add .editorconfig, add GitHub workflow (ggml-org#883)

Add enum llama_ftype, sync ggml_type to model files (ggml-org#709)

Simplify to include lower-case windows.h always, fix compile on mingw…

…32 (ggml-org#747)

ggml : add ggml_cont() + optimize ggml_cpy() for contiguous dst

ggml : fix quantize_row_q4_1() ARM_NEON (close ggml-org#876)

ggml : fix WASM build

Print model version.

Also improve model type printing, and fix indentation of an unrelated
switch statement.

cmake should link openblas properly with -lopenblas like how it's don…

…e in the makefile (ggml-org#839)

fix for windows utf-8 input (ggml-org#840)

Use UTF-16 as input on Windows, since UTF-8 does not work and reads multibyte characters as zeros