gccgo driver: always act as though -g is passed

gccgo driver: always act as though -g is passed

The go1 compiler always turns on debugging, to support Go stack traces
and functions like runtime.Callers.  With the recent switch to turn on
DWARF 5 by default, this caused failures with some versions of gas,
such as 2.35.1, because the assembly code would assume DWARF 5 but the
driver would not pass --gdwarf-5 to gas.  gas would then give an
error: "file number less than one".

This change avoids that problem by having the gccgo driver spec add a
-g option to the command line if no other -g option is present.  The
newly added -g option is passed to the assembler as --gdwarf-5.

	* gospec.c (lang_specific_driver): Add -g if no debugging options
	were passed.