crt: Fix compile of __stack_chk_guard when compiling with Link Time Optimization

At some point gcc started enforcing that __stack_chk_guard must have certain
properties, but unfortunately a side effect seems to be that the compiler
now hits an assert in its Link Time Optimizer, specifically the serializer
when __stack_chk_guard is declared in the code without being explicitly
initialized. We can just initialize it to 0 to make the assert go away.

mingw-w64-crt/ssp/ChangeLog:

	* stack_chk_guard.c (__stack_chk_guard): Initialize to 0.

Signed-off-by: TheShermanTanker <tanksherman27@gmail.com>
Reference: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126773
Signed-off-by: LIU Hao <lh_mouse@126.com>