PATH_MAX: Undefine for MinGW SDK, move long comments to github issue #937

See https://github.com/civetweb/civetweb/issues/937#issuecomment-726313638

src/civetweb.c

@@ -529,30 +529,14 @@ typedef const char *SOCK_OPT_TYPE;
 
 
 #if defined(_WIN32)
-/* The Microsoft Visual Studio SDK defines MAX_PATH, but not PATH_MAX.
- * Linux defines PATH_MAX but not MAX_PATH. MinGW defines both.
- * Linux uses UTF-8 filenames, and (typically) defines PATH_MAX as 4096
- * (see https://eklitzke.org/path-max-is-tricky).
- * Windows cannot handle UTF-8 directly but uses UCS-2 (UTF-16 without checking
- * surrogate pairs in the file API).
- * CivetWeb internally uses UTF-8 on every system, thus it needs to convert
- * all filen ames for Windows.
- * Windows has an internal limit of 259 UCS-2 characters (plus termination).
- */
-/* PATH_MAX is used in CivetWeb as char[] buffer size for UTF-8 name
- * representations. Every character in the BMP (Basic Multilingual Plane)
- * encoded as UTF-8 requires 1, 2 or 3 bytes. A BMP character encoded as
- * UTF-16 always requires one 16-bit word. A character outside the BMP
- * requires 4 bytes in UTF-8 and two 16-bit words in UTF-16 (a surrogate
- * pair).
- * Thus, a 3*259+1 bytes buffer for UTF-8 encoded text will allways be
- * sufficent to hold a 295+1 word UTF-16 encoded text.
- * We do not need 4*259+1 bytes for the UTF-8 text buffer, since none BMP
- * characters would require two words in UTF-16 and hit the UCS-2 length
- * limit of the Windows file API.
- */
-/* See also https://github.com/civetweb/civetweb/issues/937 */
-/* W_PATH_MAX is a char buffer size for 259 BMP characters in UTF-8 plus
+/* For a detailed description of these defines, see
+ * https://github.com/civetweb/civetweb/issues/937 (Nov 15, 2020). */
+
+/* The Microsoft SDK does not define PATH_MAX, but mingw does. */
+#ifdef PATH_MAX
+#undef PATH_MAX
+#endif
+/* PATH_MAX is a char buffer size for 259 BMP characters in UTF-8 plus
  * null termination, rounded up to the next 4 bytes boundary */
 #define PATH_MAX (3 * 260)
 /* W_PATH_MAX is the wchar_t buffer size required for 259 BMP characters