Support creation time access on Linux

[Screwtapello]

In nall::inode::timestamp() (a method to return some particular timestamp of some particular file), there's the following comment:

nall/inode.hpp

Lines 90 to 92 in 0bbb7d7

	//Linux simply doesn't support file creation time at all
	//this is also our fallback case for unsupported operating systems
	case time::create: return data.st_mtime;

It turns out Linux does support file-creation time, but only in the structure returned by the non-standard statx() call, not in a non-standard field returned by the stat() call.