brial and cython failed to build while building Sage

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I followed the documentation to build Sage with Debian packages.

I run the command "debian/rules prune build" and I got the following ouput:

make[3]: *** [all] Error 2
make[3]: Leaving directory '/home/alien/sagemath/sage/build/make'

real    10m4.412s
user    18m13.656s
sys 0m20.556s
***************************************************************
Error building Sage.

The following package(s) may have failed to build (not necessarily
during this run of 'make all'):

* package: brial-0.8.5
  log file: /home/alien/sagemath/sage/logs/pkgs/brial-0.8.5.log
  build directory: /home/alien/sagemath/debian/build/usr/var/tmp/sage/build/brial-0.8.5

* package: cython-0.24.1.p0
  log file: /home/alien/sagemath/sage/logs/pkgs/cython-0.24.1.p0.log
  build directory: /home/alien/sagemath/debian/build/usr/var/tmp/sage/build/cython-0.24.1.p0

    The build directory may contain configuration files and other potentially
    helpful information. WARNING: if you now run 'make' again, the build
    directory will, by default, be deleted. Set the environment variable
    SAGE_KEEP_BUILT_SPKGS to 'yes' to prevent this.

    Makefile:16: recipe for 

target 'all' failed
make[2]: *** [all] Error 1
make[2]: Leaving directory '/home/alien/sagemath/sage'

debian/rules:51: recipe for target 'override_dh_auto_build' failed
make[1]: *** [override_dh_auto_build] Error 2
make[1]: Leaving directory '/home/alien/sagemath'
debian/rules:35: recipe for target 'build' failed
make: *** [build] Error 2

Cython is already installed (Cython version 0.23.2) and I can't install brial because it depends of libstdc++6 (>= 5.2) but 4.9.2-10 will be installed.