incbin: if we have to fread(), try to do it only once...

incbin: if we have to fread(), try to do it only once...

If we can't mmap a file and instead have to fread(), if the data is
small enough that we can reasonably accomodate it in a memory buffer,
then just read it once.

It seems rather unlikely that very large files would be used with
TIMES anyway.

Also note: the previous comment about nasm_file_size[_by_path]() being
invoked twice was spurious; it does not actually happen.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>