Dpkg::BuildFlags: simplify update-buildflags hook

Pass the entire Dpkg::BuildFlags object to update-buildflags, so that
hooks can use its set() method rather than setting hash elements
directly.

scripts/Dpkg/BuildFlags.pm

@@ -84,7 +84,7 @@ sub load_vendor_defaults {
 	FFLAGS   => 'vendor',
 	LDFLAGS  => 'vendor',
     };
-    run_vendor_hook("update-buildflags", $self->{flags}, $self->{origin});
+    run_vendor_hook("update-buildflags", $self);
 }
 
 =item $bf->load_system_config()

scripts/Dpkg/Vendor/Default.pm

@@ -98,11 +98,11 @@ The hook is called in Dpkg::Changelog to post-process a
 Dpkg::Changelog::Entry after it has been created and filled with the
 appropriate values.
 
-=item update-buildflags ($flags, $origin)
+=item update-buildflags ($flags)
 
 The hook is called in Dpkg::BuildFlags to allow the vendor to override
-the default values set for the various build flags. $flags and $origin
-are hash reference.
+the default values set for the various build flags. $flags is a
+Dpkg::BuildFlags object.
 
 =back
 
@@ -122,7 +122,7 @@ sub run_hook {
     } elsif ($hook eq "extend-patch-header") {
 	my ($textref, $ch_info) = @params;
     } elsif ($hook eq "update-buildflags") {
-	my ($flags, $origin) = @params;
+	my $flags = shift @params;
     }
 
     # Default return value for unknown/unimplemented hooks

scripts/Dpkg/Vendor/Ubuntu.pm

@@ -92,9 +92,8 @@ sub run_hook {
 
     } elsif ($hook eq "update-buildflags") {
 	my $flags = shift @params;
-	my $origin = shift @params;
 	# Per https://wiki.ubuntu.com/DistCompilerFlags
-	$flags->{'LDFLAGS'} = '-Wl,-Bsymbolic-functions';
+	$flags->set('LDFLAGS', '-Wl,-Bsymbolic-functions', 'vendor');
 
     } else {
         return $self->SUPER::run_hook($hook, @params);