Fix quoting of arguments on Linux/Mac
Fix quoting of arguments on Linux/Mac

If one of the values passed to --defines includes spaces or quotes,
passing the command-line to the shell will cause the command to be
incorrectly parsed.

Since using a shell is only required on Windows, and quoting the
command-line is really tricky, only use the shell on Windows.

BUG=375811
NOTRY=true

Review URL: https://codereview.chromium.org/293053008

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@13264 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client