build-libssp: Stop building the real libssp from GCC

As mingw-w64 now provides these routines, we no longer need to build
the original library from GCC.

As building with -fstack-protector-strong still links with -lssp
(and -lssp_nonshared), we still need to provide libraries with these
names, but they can be empty dummy libraries.

Dockerfile.dev

@@ -154,8 +154,8 @@ RUN cd test && \
     done
 
 # Build libssp
-COPY build-libssp.sh libssp-Makefile ./
-RUN ./build-libssp.sh $TOOLCHAIN_PREFIX $CFGUARD_ARGS
+COPY build-libssp.sh ./
+RUN ./build-libssp.sh $TOOLCHAIN_PREFIX
 
 RUN cd test && \
     for arch in $TOOLCHAIN_ARCHS; do \