`zig cc`: consider enabling `-Wall -Werror` by default

[myaaaaaaaaa]

By default, programs like this will abort with an illegal instruction due to UBSAN:

int main() {
	int i = 100;
	i <<= i;
	return i;
}

However, programs like this will compile and run successfully:

int main() {
	int i;
	return i;
}

Since zig already enables runtime checks for undefined behavior by default, it doesn't seem like too much of a stretch to enable compile-time checks as well.

[alexrp]

The vast majority of C/C++ projects in the wild would fail to compile out of the box if we did this.

-Wall by default might be tenable, but -Werror is not.

[sagehane]

Worth noting is that #10800 currently makes it very easy to accidentally ignore compile warnings. Maybe it should be -Werror that is passed by default and passing -Wall should be up to the user?

I've previously stated my idea here: #10800 (comment)