Rework OS abstractions

- As much as possible avoid dragging system headers into translation
  units. This should avoid namespace pollution and, hopefully, speed up
  builds a little bit.

- Avoid leaning on the UCRT so much on Windows - prefer native win32
  calls and native file handles except where doing so is inconvenient
  (in particular, for stat(), which we might try and replace later).

- Also, switch from SystemFunction036 to ProcessPrng on Windows. This
  requires us to generate a stub for bcryptprimitives.dll because
  Microsoft haven't bothered to provide a link library, but the function
  is better-documented and seems to be a more direct under-the-hood call
  as well. Apparently it's what's used by the major web browsers these
  days, which seems like a good indication it's stable and trusted.

- Lastly, remove a bunch of functions and macros and stuff that weren't
  actually being used. It seems good to try and keep the scope of
  OS-dependent stuff relatively contained and only add to it when
  actually required.

1 files changed, 7 insertions, 0 deletions

diff --git a/src/stubs/bcryptprimitives.def b/src/stubs/bcryptprimitives.def
new file mode 100644
index 0000000..9021d7c
--- /dev/null
+++ b/src/stubs/bcryptprimitives.def
@@ -0,0 +1,7 @@
+; This file is dedicated to the public domain.
+
+LIBRARY bcryptprimitives
+EXPORTS
+	ProcessPrng
+
+; vi: sw=4 ts=4 noet tw=80 cc=80