Remove the last uses of mktemp and unlink/delete.

Remove the last uses of mktemp and unlink/delete.
* src/files.c (fdefines, ftable): Removed.
(defines_ostack, table_obstack): New.
Adjust dependencies of the former into uses of the latter.
* src/output.c (output_short_or_char_table, output_short_table):
Convert to using obstacks.
* src/reader.c (copy_comment2): Accept one FILE * and two
obstacks.
(output_token_defines, reader_output_yylsp): Use obstacks.
* src/system.h (obstack_fgrow3): New.