This reverts commit cc2ac1c.
This will cause master to be unstable for a while as we replace existing eio calls with uv_fs calls.
Hoist common settings into common.gypi. Restrict v8's common.gypi to v8 projects. Ensure v8 doesn't use /MP in debug builds. Add basic settings for other platforms. Make uv import common.gypi properly. Remove LTCG warning.