Update Android port

Update Android port

* src/lread.c (lread_fd, file_tell, infile, skip_dyn_bytes)
(skip_dyn_eof, readbyte_from_stdio, safe_to_load_version)
(close_infile_unwind, close_file_unwind_android_fd): New
function.
(Fload, Flocate_file_internal, openp): New argument PLATFORM.
All callers changed.
(skip_lazy_string): Add optimized versions of various functions
for accessing Android assets.