dpkg-genbuildinfo: On source builds add source to the Architecture field

debian/changelog

@@ -5,6 +5,8 @@ dpkg (1.18.15) UNRELEASED; urgency=medium
     - Do not enable PIE when linking static programs. glibc-based systems
       do not support this combination and produce very bogus output.
       Proposed by Szabolcs Nagy <nsz@port70.net>. Closes: #843714
+  * On source builds add 'source' to the Architecture field in the
+    .buildinfo file in dpkg-genbuildinfo.
   * Perl modules:
     - Validate architecture arguments in Dpkg::Deps deps_parse().
       Prompted by Johannes Schauer <josch@debian.org>.

scripts/dpkg-genbuildinfo.pl

@@ -348,6 +348,8 @@ if (build_has_any(BUILD_SOURCE)) {
     my $dsc = "${spackage}_${sversion}.dsc";
 
     $checksums->add_from_file("$uploadfilesdir/$dsc", key => $dsc);
+
+    push @archvalues, 'source';
 }
 
 my $dist_count = 0;