compilation warning in gcc 3.x

[Wenji Huang]

Hi,

There will be one compilation warning which will be treated as error in 
latest tree.

tapsets.cxx:2070: warning: converting of negative value '-0x00000001' to 
'Dwarf_Word'

This only happens on gcc 3.x, but will pass on gcc 4.x.

Seems it needs explicitly type cast:

- 	Dwarf_Word  encoding = -1;
+ 	Dwarf_Word  encoding = (Dwarf_Word)-1;

Regards,
Wenji