Don't warn for parentheses for the '&&' inside '||' for cases like:

assert(a || b && "bad");

since this is safe. This way we avoid a big source of such warnings which in this case are practically useless.

Note that we don't handle *all* cases where precedence wouldn't matter because of constants since
this is a bit costly to check, and IMO clarifying precedence with parentheses is good for
readability in general.

llvm-svn: 119533