[commit] Use bfd_byte in value.h

[Andrew Cagney]

Like I mentioned on gdb@, these are for warnings you get when building 
with GCC 4 (or for that matter, any modern compiler).  vis:

cagney@tornado$ cat -n s.c
      1  char *c;
      2  signed char *s;
      3  unsigned char *u;
      4
      5  void foo (void)
      6  {
      7    c = s;
      8    c = u;
      9    s = u;
     10  }
$ gcc --version
gcc (GCC) 4.0.0 20050412 (Red Hat 4.0.0-0.42)
...
$ gcc -c s.c
s.c: In function foo:
s.c:7: warning: pointer targets in assignment differ in signedness
s.c:8: warning: pointer targets in assignment differ in signedness
s.c:9: warning: pointer targets in assignment differ in signedness