gdb: fix missing space in some info variables output

gdb: fix missing space in some info variables output

Fixes PR gdb/28121.  When a user declares an array like this:

  int * const foo_1[3];

And in GDB the user does this:

  (gdb) info variables foo
  All variables matching regular expression "foo":

  File test.c:
  1:	int * constfoo_1[3];

Notice the missing space between 'const' and 'foo_1'.  This is fixed
in c_type_print_varspec_prefix (c-typeprint.c) by passing through the
flag that indicates if a trailing space is needed, rather than hard
coding the flag to false as we currently do.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28121