Fix MSVC CLI builds as run by the regression system.

[KineticTheory]

Background

• After upgrading to Microsoft Visual Studio 2019 16.8.0 Preview 3, the regression system could no longer build Draco due to build errors reported in system headers pulled in by rng/test. This version of MSVC also pulls in a newer version of CMake.

Purpose of Pull Request

• Fixes Redmine Issue #2168

Description of changes

• It was determined that these build errors could be eliminated by registering the rng unit tests as C++ files instead of C files, even though their file extensions are .c.
• Also add a couple of new warning suppressions for MSVC. The new version is more aggressive in reporting warnings. Only suppress issues found in the Random123 header files (we don't need to fix the TPL code).
• It was also found that the test ut_gsl provided by Random123 has a defect to most compilers are happy to ignore, but that MSVC now treats as a fatal error (a variable is declared twice in the same scope). See rng/tests/CMakeLists.txt for more details.

Status

• Reference:
  • Pre-Merge Code Review
  • CDash Status
• Checks
  • Travis/Appveyor CI checks pass
  • Code coverage does not decrease
  • Valgrind test passes
  • Toss3 checks pass
  • Trinitite checks pass
  • Code reviewed/approved, sufficient DbC checks, testing, documentation

[KineticTheory]

I'm breaking my own rules again. I'm going to merge this w/o additional review. The changes are primarily targeting the MSVC build system.