Fix GN target resolution on Windows
Fix GN target resolution on Windows

Windows drives contain a colon in their name, causing find_binary to
fail when a drive is in the PATH.

Change-Id: Ic07c86c98b9bbdc63e8711c7e7e4252cfe0d2e97

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed