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>

mingw-w64-crt/ssp/stack_chk_guard.c

diff --git a/mingw-w64-crt/ssp/stack_chk_guard.c b/mingw-w64-crt/ssp/stack_chk_guard.c
index 9d961e3..499f003 100644
--- a/mingw-w64-crt/ssp/stack_chk_guard.c
+++ b/mingw-w64-crt/ssp/stack_chk_guard.c
@@ -8,7 +8,7 @@
 #include <stdlib.h>
 #include <stdint.h>
 
-uintptr_t __stack_chk_guard;
+uintptr_t __stack_chk_guard = 0;
 
 #if defined __SSP__ || defined __SSP_STRONG__ || defined __SSP_ALL__
 // This function requires `no_stack_protector` because it changes the