The amount of time required to product a complete error/warning list for a large, broken C# solution is probably more than you'd like to spend waiting on a compile. The number isn't going to be accurate as the number of errors increase anyways, since you can easily end up in situations where hundreds of errors are caused by a single off-by-one typo; conversely, a single typo (say, an unclosed multi-line comment for a simple example) could hide many errors. Attempting to measure how long a solution will take to fix using this number is therefore useless.
But there is still a way to see what kind of mountain you have to climb -- use Resharper. Its Errors in Solution" window can be of some help with getting past the compiler limit.
Resharper isn't the only game on the block, either -- JustCode and CodeRush are both very good tools as well and are priced similarly to Resharper.
(** yes I know it's not strictly necessary for the code to run but some JS minifiers don't handle missing semicolons very well)