cli: Remove warnings as errors

[ibuclaw]

• Undocuments the -wi option
• All warnings are now counted, not just when useWarnings == error.
• Removes errorOnWarning from the driver.

The -w and -wi options still set useWarnings as error and inform respectively, this is because the "cannot inline function" warning is only diagnosed when warnings are informational. Given that druntime and phobos are built with -w, it would introduce a number of new messages when compiling.

std/internal/entropy.d(503): Warning: cannot inline function `std.internal.entropy.crashOnError`
pragma(inline, true) void crashOnError(const EntropyResult value) pure @safe
                          ^
std/math/exponential.d(4292): Warning: cannot inline function `std.math.exponential._scalbn!real._scalbn`
private F _scalbn(F)(F x, int n)
          ^
std/math/exponential.d(4292): Warning: cannot inline function `std.math.exponential._scalbn!double._scalbn`
private F _scalbn(F)(F x, int n)
          ^
std/math/exponential.d(4292): Warning: cannot inline function `std.math.exponential._scalbn!float._scalbn`
private F _scalbn(F)(F x, int n)
          ^

[dlang-bot]

Thanks for your pull request, @ibuclaw!

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Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#21780"

[ibuclaw]

Leaning towards moving -wi -> -winline to handle the "cannot inline function" informational messages. As the fact that it choses not to warn about them when warnings were treated as errors is itself odd.