[gdbsupport] Reimplement phex and phex_nz as templates

[gdbsupport] Reimplement phex and phex_nz as templates

Gdbsupport functions phex and phex_nz have a parameter sizeof_l:
...
extern const char *phex (ULONGEST l, int sizeof_l);
extern const char *phex_nz (ULONGEST l, int sizeof_l);
...
and a lot of calls use:
...
  phex (l, sizeof (l))
...

Make this easier by reimplementing the functions as a template, allowing us to
simply write:
...
  phex (l)
...

Simplify existing code using:
...
$ find gdb* -type f \
    | xargs sed -i 's/phex (\([^,]*\), sizeof (\1))/phex (\1)/'
$ find gdb* -type f \
    | xargs sed -i 's/phex_nz (\([^,]*\), sizeof (\1))/phex_nz (\1)/'
...
and manually review:
...
$ find gdb* -type f | xargs grep "phex (.*, sizeof.*)"
$ find gdb* -type f | xargs grep "phex_nz (.*, sizeof.*)"
...

Tested on x86_64-linux.

Approved-By: Tom Tromey <tom@tromey.com>