[gdb/testsuite] Fix gdb.ada/literals.exp with aarch64

On aarch64-linux, I run into:
...
(gdb) print 16#ffffffffffffffff#^M
$7 = 18446744073709551615^M
(gdb) FAIL: gdb.ada/literals.exp: print 16#ffffffffffffffff#
...
while on x86_64-linux instead, I get:
...
(gdb) print 16#ffffffffffffffff#^M
$7 = -1^M
(gdb) PASS: gdb.ada/literals.exp: print 16#ffffffffffffffff#
...

We can easily reproduce this on x86_64-linux using:
...
$ gdb -q -batch -ex "set lang ada" -ex "set arch i386" \
  -ex "print 16#ffffffffffffffff#"
$1 = -1
$ gdb -q -batch -ex "set lang ada" -ex "set arch aarch64" \
  -ex "print 16#ffffffffffffffff#"
$1 = 18446744073709551615
...

With i386, we have:
...
(gdb) p int_bits
$3 = 32
(gdb) p long_bits
$4 = 32
(gdb) p long_long_bits
$5 = 64
...
and so in processInt we hit the fits-in-unsigned-long-long case where we use
as type long long:
...
      /* Note: Interprets ULLONG_MAX as -1.  */
      yylval.typed_val.type = type_long_long (par_state);
...

With aarch64, we have instead:
...
(gdb) p int_bits
$1 = 32
(gdb) p long_bits
$2 = 64
(gdb) p long_long_bits
$3 = 64
...
and so in processInt we hit the fits-in-unsigned-long case where we use
as type unsigned long:
...
      yylval.typed_val.type
        = builtin_type (par_state->gdbarch ())->builtin_unsigned_long;
...

It's not clear why for ada we're using long long for the
fits-in-unsigned-long-long case.

Fix this by using unsigned long long for the fits-in-unsigned-long-long case,
meaning the new reference output is 18446744073709551615 instead of -1.

Tested on x86_64-linux.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29416

gdb/ada-lex.l

@@ -498,8 +498,8 @@ processInt (struct parser_state *par_state, const char *base0,
     yylval.typed_val.type = type_long_long (par_state);
   else if (fits_in_type (1, value, long_long_bits, false))
     {
-      /* Note: Interprets ULLONG_MAX as -1.  */
-      yylval.typed_val.type = type_long_long (par_state);
+      yylval.typed_val.type
+	= builtin_type (par_state->gdbarch ())->builtin_unsigned_long_long;
       /* See unsigned long case above.  */
       if (value & LONGEST_SIGN)
 	yylval.typed_val.val =

gdb/testsuite/gdb.ada/literals.exp

@@ -36,4 +36,4 @@ gdb_test "print 16#f#e1" " = 240"
 gdb_test "print 16#1#e10" " = 1099511627776"
 
 gdb_test "print/x 16#7fffffffffffffff#" " = 0x7fffffffffffffff"
-gdb_test "print 16#ffffffffffffffff#" " = -1"
+gdb_test "print 16#ffffffffffffffff#" " = 18446744073709551615"