winpthreads: move definition of WIN32_LEAN_AND_MEAN from Makefile.am to source files

All #include directives in source files and internal header files
have been grouped in following order:

- CRT header files
- Windows API header files
- winpthreads' public header files
- winpthreads' internal header files

In each group, header files are sorted alphabetically.

Unnecessary includes have been removed from internal header files.

Signed-off-by: Kirill Makurin <maiddaisuki@outlook.com>
Signed-off-by: LIU Hao <lh_mouse@126.com>
17 files changed