Master issue for MinGW-w64 TaskDialog() linker failures

Apparently MinGW-w64 v4 and lower do not include TaskDialog(). Because Go currently requires gcc or compatible (e.g. clang) to build with cgo, we'll need to address this, especially since MinGW-w64 is separate from the original MinGW, and especially since some people might have installed MinGW or MinGW-w64 as part of a larger package (such as an IDE like Code::Blocks). Some people have also confused the version of MinGW-w64 with the version of gcc, which also doesn't help things.

I originally thought I fixed this in MinGW-w64 4, but apparently that only got propagated to MSYS2, not MinGW-w64 binary releases. I don't know what the current scenario is, but I will definitely need to get solid version numbers that I can test against...

I could alternatively switch to `TaskDialogIndirect()`, which IIRC (**I could be wrong about this; I forget now**) does not have this issue, but that **might** (does not have to, but would be nice if it was) be contingent on reworking dialogs, which I have to make an issue about, but the general gist of my dilemma can be read [here](https://github.com/kusti8/proton-native/issues/47#issuecomment-373068947). I also forget if `TaskDialogIndirect()` behaves differently from `TaskDialog()` with regards to the limit on the amount of text in the dialog and the line wrapping rules therein.

(There's also dynamically loading `TaskDialog()`, which is a bit overkill, but eh.)

There are a lot of people using TDM-GCC instead of MinGW-w64. I need to investigate whether that one can be used for post-Windows 2000 code at all, otherwise I have to start explicitly looking for TDM specifically to give a special error message in that case (in addition to a non-MinGW-w64 MinGW error message).

I might convert this into a tracking issue later.