The following error occurs when using `rake -m` on AppVeyor:
```
fatal error C1041: cannot open program database 'C:\projects\mruby\vc140.pdb'; if multiple CL.EXE write to the same .PDB file, please use /FS
```
Therefore, the issue is solved by not creating the PDB file. It is expected
to be somewhat faster by not generating debugging information (I don't think
debugging information is necessary for normal CI).
The `debug` build target (`MRB_GC_STRESS` is enabled) on CI have been
compiled but not tested so far. However, I think testing with
`MRB_GC_STRESS` is effective (in fact, I found #4907 bug).
Therefore, I integrated `debug` and `full-debug` build targets to enable
`MRB_GC_STRESS` testing. Testing with `MRB_GC_STRESS` takes a little time,
but compiling takes more time, so CI execution time does not increase due to
decrease of build target.
KOBAYASHI Shuji