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[Bug debug/12500] stabs debug info -- void no longer a predefined / builtin type

[drow at mvista dot com requested that I send this to gcc-patches.
This is already filed in the gcc bug database as debug/12500.

This is a regression relative to (at least) 2.95.3.]

[Observed in i686-pc-linux-gnu native and i686-pc-linux-gnu x powerpc-elf-eabi;
but problem is really configuration independent.]

Pick your favorite .c file, compile it with -gstabs -S, and examine
the output.  At the top of the file you will find the stabs entries
for the predefined / builtin data types -- int, char, short, long,
et cetera.  In 2.95.3, the list included 'void'; in 3.3.1, void is
absent.  This causes subsequent errors in the debug information for
functions and variables that reference void.

The fix is a one liner -- file gcc/dbxout.c, function dbxout_typedefs,
change the line:

    && COMPLETE_TYPE_P (type)

With this patch, it bootstraps just fine.

BTW, I consider my one line fix to be low risk because:

. it does not affect code generation for ANY targets, regardless of
  the command line options

. it only affects stabs debug information

. the function modified is only called once; and it only produces one
additional line of stabs output -- a line of output that was present in

. the compiler bootstraps just fine

. void was the only deletion; and it appears to have been done
accidentally as a side effect of another change (so, I believe that
putting it back is "the right fix").

. we are using it in house and it works

NOTE: The problem was initially observed internally using a locally
written stabs parser.

I believe that there were structs containing pointers to void and they
got mis-represented as either instances of non-existent types or self
referential types or some such.

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