* Respect WARNINGS_AS_ERRORS option for msvc builds.

* Disable a bunch of warnings for msvc builds. These were gathered from
  all the hand-crafted vcxproj files and merged into one set. Eventually
  we need to disable some of these and fix the actual warnings.

* Treat specific warnings as errors for msvc builds. These were gathered
  from the hand-crafted vcxproj files.

* Fix LLVM build showing warning 4141 despite being disabled in
  CMakeLists. Something wonky happens when using set with the first
  string argument. Going with list(APPEND,...) works, and is symmetrical
  with the non-msvc script.

* Define _SCL_SECURE_NO_WARNINGS for all modules, not just LLVM.

* Fix double to float conversion warning in SprivShader.cpp

* Fix mismatched type compare in IceTargetLoweringX664Traits.h

Bug: b/132445520
Change-Id: I1143e9fdd386e26d4f0b0f9e34c4d6b3ac2f2311
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/31149
Presubmit-Ready: Antonio Maiorano <amaiorano@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>