Appveyor: run nmake with defining DEBUG

[masatake]

• msbuild
• msvc
• mingw

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (23d444c) 83.04% compared to head (2a910c8) 83.04%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3801   +/-   ##
=======================================
  Coverage   83.04%   83.04%           
=======================================
  Files         227      227           
  Lines       55203    55203           
=======================================
  Hits        45843    45843           
  Misses       9360     9360           

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[masatake]

I should verify the other runtime?/compiler combinations.
However, this change may be needed in the development of the V parser, so I merge this.