Makes analyzer strip off a leading path separator

When running in chrome paths are absolute.

Also makes chrome build work with analyzer on windows. The specific define I
ran into was MSVS_OS_BITS, but I'm sure there are more.

BUG=chromium:383609
R=mark@chromium.org

Patch by Scott Violet <sky@chromium.org>
Review URL: https://codereview.chromium.org/347193005/


git-svn-id: http://gyp.googlecode.com/svn/trunk@1946 78cadc50-ecff-11dd-a971-7dbc132099af