[gdb/exp] Fix ptype $_creal/$_cimag

Consider test.c, compiled with -g:
...
__complex__ float cf = 1 + 2i;
int main (void) { return 0; }
...

The values of cf and its components are:
...
$ gdb -q a.out
Reading symbols from a.out...
(gdb) p cf
$1 = 1 + 2i
(gdb) p $_creal(cf)
$2 = 1
(gdb) p $_cimag(cf)
$3 = 2
...
and their respective types are:
...
(gdb) ptype $1
type = complex float
(gdb) ptype $2
type = float
(gdb) ptype $3
type = float
...

Now let's try that again, using ptype directly:
...
(gdb) ptype cf
type = complex float
(gdb) ptype $_creal(cf)
type = int
(gdb) ptype $_cimag(cf)
type = int
...

The last two types should have been float, not int.

Fix this by extending the internal function handlers creal_internal_fn and
cimag_internal_fn with the noside parameter, such that we get instead:
...
(gdb) ptype $_creal(cf)
type = float
(gdb) ptype $_cimag(cf)
type = float
...

Tested on x86_64-linux.

Reviewed-By: Keith Seitz <keiths@redhat.com>

PR exp/31816
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31816