fix: ignore failure of GetCompilerPredefines

[toyobayashi]

fixes #294
fixes nodejs/node-gyp#3164

[Ben08300]

Hi,
Just wanted to tell that I've tested the above changes.

Compilation now runs smoothly and just displays a warning (which is expected according to the PR):

Warning: failed to get compiler predefines
cmd: ['cl.exe', '-dM', '-E', '-x', 'c', 'C:\\Users\\benja\\AppData\\Local\\Temp\\tmp0rvxkp3m.c']
status: 2

Any ETA regarding the next gyp-next and node-gyp releases ?
Thanks again for your reactivity.

[legendecas]

Would you mind adding a test case covering that the command fails? Thank you!

[toyobayashi]

Done.