[compiler-rt][builtins] Fix `-Werror` build problem (#100312)
GCC-14.1.1 emit an error due to uninitialized variables
x86.c:303:17: error: ‘EAX’ may be used uninitialized
[-Werror=maybe-uninitialized]
x86.c:970:35: error: ‘MaxLevel’ may be used uninitialized
[-Werror=maybe-uninitialized]
x86.c:987:48: error: ‘MaxExtLevel’ may be used uninitialized
[-Werror=maybe-uninitialized]
It doesn't handle properly that these variables initialized indirectly
in functions that takes pointers to them