google-breakpad: disable on mips64

Due to some mmap() related issue, google-breakpad fails to build on
mips64, so let's disable it for the moment. The mips/mips64 folks
might be interested in fixing that later.

Fixes:

  http://autobuild.buildroot.org/results/2b0/2b03937693ea400ddcc7e8364ff7dc22ce651669/



Cc: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Cc: Markos Chandras <Markos.Chandras@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>