Improve check for packing quad values

- Check if quad values can be packed by using `eval`. This is because
  the condition for whether `pack` can use quad values is a bit more
  complicated. See:

    * <https://www.nntp.perl.org/group/perl.perl5.porters/2013/10/msg208380.html>,
    * <Perl/perl5@1640b98>,
    * <Perl/perl5@c174bf3>

- Add unsigned quad value (Q) to the condition.

- Also check for pack("D", ...) directly. This simplifies the check and
  removes the need for checking against the Perl version.

Basic/Core/Core.pm

@@ -16,12 +16,11 @@ use Config;
 use List::Util qw(max);
 use Scalar::Util 'blessed';
 
+# If quad (q/Q) is available for pack().
+our $CAN_PACK_QUAD = !! eval { my $packed = pack "Q", 0; 1 };
+
 # If "D" is available for pack().
-# See commit <https://github.com/Perl/perl5/commit/77a2054ea312b030904555167b764e4510dbcac6>
-# and PR <https://github.com/Perl/perl5/pull/18517>.
-our $CAN_PACK_D =
-  ( $^V < v5.33.7 && $Config{d_longdbl} && $Config{uselongdouble} )
-  || ( $^V >= v5.33.7 && $Config{d_longdbl} );
+our $CAN_PACK_D = !! eval { my $packed = pack "D", 0; 1 };
 
 our @EXPORT = qw( piddle pdl null barf ); # Only stuff always exported!
 my @convertfuncs = map $_->convertfunc, PDL::Types::types();
@@ -1204,7 +1203,7 @@ sub PDL::new {
          # new was passed a string argument that doesn't look like a number
          # so we can process as a Matlab-style data entry format.
 		return PDL::Core::new_pdl_from_string($new,$value,$this,$type);
-      } elsif ($Config{ivsize} < 8 && $pack[$new->get_datatype] eq 'q*') {
+      } elsif (! $CAN_PACK_QUAD && $pack[$new->get_datatype] =~ /^q\*$/i ) {
          # special case when running on a perl without 64bit int support
          # we have to avoid pack("q", ...) in this case
          # because it dies with error: "Invalid type 'q' in pack"