Series of windows fixes.

This contains a series of fixes to make sure the source can compile with
clang-cl under windows.

- Updates to include specific headers
- Define constants
- Iterate over path v.s. using regex.
- Initialize random generator with unsigned int.

Bug: 186567864
Test: gd/cert/run
Change-Id: I9049573befd459a7149bb2e3625e90ae0f46de3d