package/gcc: disable libsanitizer with gcc 7.5 and glibc 2.31 toolchain

package/gcc: disable libsanitizer with gcc 7.5 and glibc 2.31 toolchain

libsanitizer in gcc 7.x fails to build with glibc 2.31. Fixing it would
require backporting an upstream commit:

    https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=4abc46b51af5751d657764d0c44b8a4aeed06302

However, the backport is not trivial, as there are a lot of conflicts.

Disable libsanitizer since the gcc 7.5 branch is now closed
(unmaintained) and it's not a trivial merge.

Signed-off-by: Romain Naour <romain.naour@smile.fr>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>