* gcc.c: Move data on prefixes forward in file and reorganize.
(md_exec_prefix, md_startfile_prefix, md_startfile_prefix_1):
Always define, but make null if no value.
(static_specs): Add "md_exec_prefix", "md_startfile_prefix",
and "md_startfile_prefix_1".
(main): Check whether md_exec_prefix and the others are the
null string rather than whether the macro is defined.
From-SVN: r36730
