In option typo correction, consider -foo=VALUE flags as two distinct parts. The

comments claimed it did this, but the LHS value was actually an unused variable.

The new system considers only the '-foo' part when comparing it for typos
against flags that have values, but still look at the whole string for flags
that don't. That way, we'll still correct '-inst=combine' to '-instcombine'.

llvm-svn: 130685