add -wc-analyze option

example usage:

echo "int main(){int *x=0; *x=0; return 0;}" | w32-clang -wc-analyze -xc -
<stdin>:1:25: warning: Dereference of null pointer (loaded from variable 'x')
int main(){ int *x=0; *x=0; return 0;}
                        ~^
<stdin>:1:13: note: 'x' initialized to a null pointer value
int main(){ int *x=0; *x=0; return 0;}
            ^~~~~~
<stdin>:1:25: note: Dereference of null pointer (loaded from variable 'x')
int main(){ int *x=0; *x=0; return 0;}
                        ~^
1 warning generated.