cc/gcc: add option to enable/disable libsanitizer

libsaniotizer requires a few headers that are not in uClibc, for
example. Also, it is only available for native threads (NPTL under
glibc.) Finally, it is only available starting with gcc-4.8.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>