gcc: disable libsanitizer for sparc

Normally libsanitizer handles the different functionalities gracefully for
each architecture, but it doesn't seem to be the case for SPARC.
Since in general it doesn't support anything for SPARC just disable it.

Fixes bug #7951.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>