stabs for local variables does not work on x86-64

[Peter Vreman]

When compiling a simple program with gcc -gstabs the values of locals
can't be read. The problem is that the 32bit value from the stabs is
readed as unsigned instead of signed. The result is that locals on e.g. -8
are for gdb on offset 0xfffffff8. A quick test with changing the macro
INTERNALIZE_SYMBOL in dbxread.c to read the 32bit value as signed makes
the printing of local variables working.

Peter