mv include/ruby/{impl,internal}

Devs do not love "impl".

include/ruby/internal/dosish.h

@@ -0,0 +1,63 @@
+#ifndef RBIMPL_DOSISH_H                              /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_DOSISH_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries. They could be written in C++98.
+ * @brief      Support for so-called dosish systems.
+ */
+#ifdef __CYGWIN__
+#undef _WIN32
+#endif
+
+#if defined(_WIN32)
+/*
+  DOSISH mean MS-Windows style filesystem.
+  But you should use more precise macros like DOSISH_DRIVE_LETTER, PATH_SEP,
+  ENV_IGNORECASE or CASEFOLD_FILESYSTEM.
+ */
+#define DOSISH 1
+# define DOSISH_DRIVE_LETTER
+#endif
+
+#ifdef _WIN32
+#include "ruby/win32.h"
+#endif
+
+#if defined(DOSISH)
+#define PATH_SEP ";"
+#else
+#define PATH_SEP ":"
+#endif
+
+#define PATH_SEP_CHAR PATH_SEP[0]
+
+#define PATH_ENV "PATH"
+
+#if defined(DOSISH)
+#define ENV_IGNORECASE
+#endif
+
+#ifndef CASEFOLD_FILESYSTEM
+# if defined DOSISH
+#   define CASEFOLD_FILESYSTEM 1
+# else
+#   define CASEFOLD_FILESYSTEM 0
+# endif
+#endif
+
+#endif /* RBIMPL_DOSISH_H */