Removed use of unused LDPATH variable on Windows as is done for other platforms, and added GCC flag to ensure MINGW's ANSI compatible STDIO functions are used wherever available (required by jemalloc).
Without these changes it ends up setting the PATH twice, and the second time the PATH begins with `:` which is invalid. Also the regular msvcrt printf-like functions would be used which don't understand stuff like %hhd and %z which jemalloc uses.
This change ought not to make any difference to the output but it fixes the build process for me since at least my build environment couldn't handle that broken path caused by LDPATH being empty.
710dcdc2eb