what is the meaning of set the macro LV_FS_POSIX_PATH to ./

If you selected posix filesystem (define LV_FS_IF_POSIX a drive letter), that sets base path for this filesystem. ./ is default if not previously specified if you see code below. win32 default is backslash

see below links for reference:
old readme:

edit: the links for code I pasted are actually old (I think), here is latest from master: