Add option for paranoid unsafe path checking

This commit adds a Config.in option to the "Build options" submenu to
enable paranoid checking of unsafe paths. This mechanism is added as
an option so that when we'll enable it in the autobuilders, people
trying to reproduce the build failures will be able to do so by just
downloading the configuration file. If instead we were leaving this
feature as an environment variable, everyone would have to remember to
pass this environment variable to reproduce build issues. And certain
build issues triggered by paranoid unsafe patch checking may not be
visible in the build output, for example when they happen during the
execution of configure scripts.

Since this option is fairly advanced, a new submenu inside "Build
options" is created, for Advanced options.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Reviewed-by: Romain Naour <romain.naour@openwide.fr>
Tested-by: Romain Naour <romain.naour@openwide.fr>