scripts: Use error() and errormsg() instead of printing on STDERR directly

This way any transformation done for error messages gets applied
consistently to all error output.

scripts/Dpkg/Source/Package/V1.pm

@@ -403,8 +403,7 @@ sub do_build {
     }
 
     if ($ur) {
-        printf { *STDERR } g_('%s: unrepresentable changes to source') . "\n",
-               $Dpkg::PROGNAME;
+        errormsg(g_('unrepresentable changes to source'));
         exit(1);
     }
 }

scripts/dpkg-checkbuilddeps.pl

@@ -138,12 +138,12 @@ if ($bc_value) {
 }
 
 if (@unmet) {
-	printf { *STDERR } g_('%s: Unmet build dependencies: '), $Dpkg::PROGNAME;
-	print { *STDERR } join(' ', map { $_->output() } @unmet), "\n";
+	error(g_('Unmet build dependencies: %s'),
+	      join(' ', map { $_->output() } @unmet));
 }
 if (@conflicts) {
-	printf { *STDERR } g_('%s: Build conflicts: '), $Dpkg::PROGNAME;
-	print { *STDERR } join(' ', map { $_->output() } @conflicts), "\n";
+	error(g_('Build conflicts: %s'),
+	      join(' ', map { $_->output() } @conflicts));
 }
 exit 1 if @unmet || @conflicts;