buildtools/wafsamba: add --disable-stack-protector option

Allow the user to disable stack-protector through --disable-stack-protector to avoid the following build failure with libtalloc on embedded toolchains which don't support stack-protector:

/home/autobuild/autobuild/instance-5/output-1/host/lib/gcc/i686-buildroot-linux-musl/9.4.0/../../../../i686-buildroot-linux-musl/bin/ld: talloc.c.5.o: in function `_vasprintf_tc':
talloc.c:(.text+0x427d): undefined reference to `__stack_chk_fail_local'

This build failure is raised since ffontaine/samba@38e97f8b because stack-protector is enabled on libtalloc despite the fact that libssp is not available:

Checking if compiler accepts -fstack-protector-strong                                           : yes

Fixes:

• http://autobuild.buildroot.org/results/e221bde25c7622db99761d0adcd56663296beb15

Signed-off-by: Fabrice Fontaine fontaine.fabrice@gmail.com