build: Build the bootstrap tarballs on Hydra.

* build-aux/hydra/gnu-system.scm (%packages-to-cross-build): Uncomment
  the bootstrap tarball packages.

build-aux/hydra/gnu-system.scm

@@ -79,12 +79,11 @@ (define (package-cross-job store job-name package target system)
 (define %packages-to-cross-build
   (list gmp mpfr mpc coreutils findutils diffutils patch sed grep
         gawk gettext hello guile-2.0
-        ;; %bootstrap-binaries-tarball
-        ;; %binutils-bootstrap-tarball
-        ;; %glibc-bootstrap-tarball
-        ;; %gcc-bootstrap-tarball
-        ;; %guile-bootstrap-tarball
-        ))
+        %bootstrap-binaries-tarball
+        %binutils-bootstrap-tarball
+        %glibc-bootstrap-tarball
+        %gcc-bootstrap-tarball
+        %guile-bootstrap-tarball))
 
 (define %cross-targets
   '("mips64el-linux-gnu"))